Abbreviated structural formula and skeletal formula.

This molecule has two different functional groups, an alkene and an alkyne

It has E/Z isomers based on carbon atom 4.

From the CIP assignment priority rule for E/Z isomers: ₆C  >  ₁H

CIP rule for the four atoms/groups around the >C=C< double bond

Other names applicable: 1-hexen-4-yne, (E)-hex-4-en-1yne, (4E)-hex-4-en-1yne, (Z)-hex-4-en-1yne, (4Z)-hex-4-en-1yne, (E)-1-hexen-4-yne, (4E)-1-hexen-4-yne, (Z)-1-hexen-4-yne, (4Z)-1-hexen-4-yne

Number of low resolution NMR chemical shift δ signal peaks: 5 ¹H and 6 ¹³C (email if disagree?)

¹H NMR ratio of peaks: 1 : 2 : 1 : 1 : 3 (for equivalent protons)

(3) hex-5-en-1-yne, HC≡CCH₂CH₂CH=CH₂, HC≡C-CH₂-CH₂-CH=CH₂ ,

Abbreviated structural formula and skeletal formula, both an alkene and alkyne.

Other names applicable:  1-hexen-5-yne

Number of low resolution NMR chemical shift δ signal peaks: 5 ¹H and 6 ¹³C (email if disagree?)

¹H NMR ratio of peaks: 1 : 2 : 2 : 1 : 2 (for equivalent protons)

BUT, for the 'end' =CH₂ alkene protons, you can get two chemical shifts close together, if there are two different groups attached to the other carbon of the C=C bond i.e. R"R'C=CH₂ where R" and R' are different. This causes the two =CH₂ protons to experience slightly different fields.

(4) hex-2-en-4-yne, H₃CC≡CCH=CHCH₃, H₃C-C≡C-CH=CH-CH₃,

Abbreviated structural formula and skeletal formula, both an alkene and alkyne.

IUPAC rule is that en takes the lowest number above yne, but, the suffix yne is still higher ranking than ene in IUPAC nomenclature.

E/Z isomers based on carbon atom 4

CIP assignment priority rule for E/Z isomers: ₆C  >  ₁H

CIP rule for the four atoms/groups around the >C=C< double bond

Other names applicable: 2-hexen-5-yne, (E)-hex-2-en-4-yne, (4E)-hex-2-en-4-yne, (Z)-hex-2-en-4-yne, (4Z)-hex-2-en-4-yne, (E)-2-hexen-5-yne, (4E)-2-hexen-5-yne, (Z)-2-hexen-5-yne, (4Z)-2-hexen-5-yne

Number of low resolution NMR chemical shift δ signal peaks: 4 ¹H and 6 ¹³C (email if disagree?)

¹H NMR ratio of peaks: 3 : 1 : 1 : 3 (for equivalent protons)

(5) hex-1-en-4-yne, H₃CC≡CCH₂CH=CH₂, H₃C-C≡C-CH₂-CH=CH₂,

Abbreviated structural formula and skeletal formula, both an alkene and alkyne.

Other names applicable: 1-hexen-4-yne

Number of low resolution NMR chemical shift δ signal peaks: 4 ¹H and 6 ¹³C (email if disagree?)

¹H NMR ratio of peaks: 3 : 2 : 1 : 2 (for equivalent protons)

BUT, for the 'end' =CH₂ alkene protons, you can get two chemical shifts close together, if there are two different groups attached to the other carbon of the C=C bond i.e. R"R'C=CH₂ where R" and R' are different. This causes the two =CH₂ protons to experience slightly different fields.

(6) hex-1-en-3-yne, H₃CCH₂C≡CCH=CH₂, H₃C-CH₂-C≡C-CH=CH₂,

Abbreviated structural formula and skeletal formula, both an alkene and alkyne.

Other names applicable: 1-hexen-3-yne

Number of low resolution NMR chemical shift δ signal peaks: 4 ¹H and 6 ¹³C (email if disagree?)

¹H NMR ratio of peaks: 3 : 2 : 1 : 2 (for equivalent protons)

BUT, for the 'end' =CH₂ alkene protons, you can get two chemical shifts close together, if there are two different groups attached to the other carbon of the C=C bond i.e. R"R'C=CH₂ where R" and R' are different. This causes the two =CH₂ protons to experience slightly different fields.

(7) 2-methylpent-2-en-4-yne, HC≡CCH=C(CH₃)₂, HC≡C-CH=C(CH₃)₂,

Abbreviated structural formula and skeletal formula, both an alkene and alkyne, but carbon chain now branched.

Other names applicable: 2-methyl-2-penten-4-yne

Number of low resolution NMR chemical shift δ signal peaks: 3 ¹H and 5 ¹³C (email if disagree?)

¹H NMR ratio of peaks: 1 : 1 : 6 (for equivalent protons)

(8) 2-methylpent-1-en-4-yne, HC≡CCH₂C(CH₃)=CH₂, HC≡C-CH₂-C(CH₃)=CH₂,

Abbreviated structural formula and skeletal formula, both an alkene and alkyne, but carbon chain now branched.

Other names applicable: 2-methyl-1-penten-4-yne

Number of low resolution NMR chemical shift δ signal peaks: 4 ¹H and 6 ¹³C (email if disagree?)

¹H NMR ratio of peaks: 1 : 2 : 3 : 2 (for equivalent protons)

BUT, for the 'end' =CH₂ alkene protons, you can get two chemical shifts close together, if there are two different groups attached to the other carbon of the C=C bond i.e. R"R'C=CH₂ where R" and R' are different. This causes the two =CH₂ protons to experience slightly different fields.

(9) 3-methylenepent-1-yne, HC≡CC(=CH₂)CH₂CH₃, HC≡C-C(=CH₂)-CH₂-CH₃,

Abbreviated structural formula and skeletal formula, both an alkene and alkyne, but carbon chain now branched.

Other names applicable: 3-methylene-1-pentyne

Number of low resolution NMR chemical shift δ signal peaks: 4 ¹H and 6 ¹³C (email if disagree?)

¹H NMR ratio of peaks: 1 : 2 : 2 : 3 (for equivalent protons)

BUT, for the 'end' =CH₂ alkene protons, you can get two chemical shifts close together, if there are two different groups attached to the other carbon of the C=C bond i.e. R"R'C=CH₂ where R" and R' are different. This causes the two =CH₂ protons to experience slightly different fields.

(10) 2-methylpent-1-en-3-yne, H₃CC≡CC(CH₃)=CH₂, H₃C-C≡C-C(CH₃)=CH₂,

Abbreviated structural formula and skeletal formula, both an alkene and alkyne, but carbon chain now branched.

Other names applicable: 2-methyl-1-penten-3-yne

Number of low resolution NMR chemical shift δ signal peaks: 3 ¹H and 6 ¹³C (email if disagree?)

¹H NMR ratio of peaks: 3 : 3 : 2 (for equivalent protons)

BUT, for the 'end' =CH₂ alkene protons, you can get two chemical shifts close together, if there are two different groups attached to the other carbon of the C=C bond i.e. R"R'C=CH₂ where R" and R' are different. This causes the two =CH₂ protons to experience slightly different fields.

(11) hexa-1,2,3-triene, H₂C=C=C=CHCH₂CH₃, H₂C=C=C=CH-CH₂-CH₃,

Abbreviated structural formula and skeletal formula, three alkene groups connected in series.

Other names applicable: 1,2,3-hexatriene

Number of low resolution NMR chemical shift δ signal peaks: 4 ¹H and 6 ¹³C (email if disagree?)

¹H NMR ratio of peaks: 2 : 1 : 2 : 3 (for equivalent protons)

BUT, for the 'end' =CH₂ alkene protons, you can get two chemical shifts close together, if there are two different groups attached to the other carbon of the C=C bond i.e. R"R'C=CH₂ where R" and R' are different. This causes the two =CH₂ protons to experience slightly different fields.

(12) hexa-1,2,4-triene, H₂C=C=CHCH=CHCH₃, H₂C=C=CH-CH=CH-CH₃,

Abbreviated structural formula and skeletal formula, an alkene - a triene (triple C=C bond) grouping.

E/Z isomers based on carbon atom 4.

CIP assignment priority rule for E/Z isomers: ₆C  >  ₁H

CIP rule for the four atoms/groups around the >C=C< double bond

Other names applicable: 1,2,4-hexatriene, (E)-hexa-1,2,4-triene, (4E)-hexa-1,2,3-triene, (Z)-hexa-1,2,4-triene, (4Z)-hexa-1,2,3-triene, (E)-1,2,4-hexatriene, (4E)-1,2,4-hexatriene, (Z)-1,2,4-hexatriene, (4Z)-1,2,4-hexatriene

Number of low resolution NMR chemical shift δ signal peaks: 5 ¹H and 6 ¹³C (email if disagree?)

¹H NMR ratio of peaks: 2 : 1 : 1 : 1 : 3 (for equivalent protons)

BUT, for the 'end' =CH₂ alkene protons, you can get two chemical shifts close together, if there are two different groups attached to the other carbon of the C=C bond i.e. R"R'C=CH₂ where R" and R' are different. This causes the two =CH₂ protons to experience slightly different fields.

(13) hexa-1,2,5-triene, H₂C=C=CHCH₂CH=CH₂, H₂C=C=CH-CH₂-CH=CH₂,

Abbreviated structural formula and skeletal formula, an alkene - a triene (triple C=C bond) grouping.

Other names applicable: 1,2,5-hexatriene

Number of low resolution NMR chemical shift δ signal peaks: 5 ¹H and 6 ¹³C (email if disagree?)

¹H NMR ratio of peaks: 2 : 1 : 2 : 1 : 2 (for equivalent protons)

BUT, for the 'end' =CH₂ alkene protons, you can get two chemical shifts close together, if there are two different groups attached to the other carbon of the C=C bond i.e. R"R'C=CH₂ where R" and R' are different. This causes the two =CH₂ protons to experience slightly different fields.

(14) hexa-1,3,5-triene, H₂C=CH-CH=CH-CH=CH₂,

Abbreviated structural formula and skeletal formula, note the symmetry of the molecule, which significantly reduces the number of NMR chemical shifts.

The molecule has three alkene groups all separated from each other - a triene (triple C=C bond) grouping.

CIP assignment priority rule for E/Z isomers: ₆C  >  ₁H

CIP rule for the four atoms/groups around the >C=C< double bond

Other names applicable: 1,3,5-hexatriene, (E)-hexa-1,3,5-triene, (3E)-hexa-1,3,5-triene, (Z)-hexa-1,3,5-triene, (3Z)-hexa-1,3,5-triene, (E)-1,3,5-hexatriene, (3E)-1,3,5-hexatriene, (Z)-1,3,5-hexatriene, (3Z)-1,3,5-hexatriene

CIP assignment priority rule for E/Z isomers: ₆C  >  ₁H

Number of low resolution NMR chemical shift δ signal peaks: 3 ¹H and 3 ¹³C (email if disagree?)

¹H NMR ratio of peaks: 4 (2x2) : 2 (2x1) : 2 (2x1) = 2 : 1 : 1 (for equivalent protons)

BUT, for the 'end' =CH₂ alkene protons, you can get two chemical shifts close together, if there are two different groups attached to the other carbon of the C=C bond i.e. R"R'C=CH₂ where R" and R' are different. This causes the two =CH₂ protons to experience slightly different fields.

(15) hexa-2,3,4-triene, H₃CCH=C=C=CHCH₃, H₃C-CH=C=C=CH-CH₃,

Abbreviated structural formula and skeletal formula, three alkene groups connected in series (triene).

Other names applicable: 2,3,4-hexatriene and no E/Z or R/S isomers

Number of low resolution NMR chemical shift δ signal peaks: 2 ¹H and 3 ¹³C (email if disagree?)

¹H NMR ratio of peaks: 6 (2x3) : 2 (2x1) = 3 : 1 (for equivalent protons)

(16) 4-methylpenta-1,2,3-triene, H₂C=C=C=C(CH₃)₂,

Abbreviated structural formula and skeletal formula, three alkene groups connected in series (triene) with chain branching.

Other names applicable: 4-methyl-1,2,3-pentatriene

Number of low resolution NMR chemical shift δ signal peaks: 2 ¹H and 5 ¹³C (email if disagree?)

¹H NMR ratio of peaks: 2 : 6 (2x3) = 1 : 3 (for equivalent protons)

BUT, for the 'end' =CH₂ alkene protons, you can get two chemical shifts close together, if there are two different groups attached to the other carbon of the C=C bond i.e. R"R'C=CH₂ where R" and R' are different. This causes the two =CH₂ protons to experience slightly different fields.

(17) 3-methylpenta-1,2,4-triene, H₂C=C=C(CH₃)CH=CH₂, H₂C=C=C(CH₃)-CH=CH₂,

Abbreviated structural formula and skeletal formula, a diene formation and alkene groupings, with chain branching, but a triene overall.

Other names applicable: 3-methyl-1,2,4-pentatriene

Number of low resolution NMR chemical shift δ signal peaks: 4 ¹H and 6 ¹³C (email if disagree?)

¹H NMR ratio of peaks: 2 : 3 : 1 : 2 (for equivalent protons)

BUT, for the 'end' =CH₂ alkene protons, you can get two chemical shifts close together, if there are two different groups attached to the other carbon of the C=C bond i.e. R"R'C=CH₂ where R" and R' are different. This causes the two =CH₂ protons to experience slightly different fields.

(18) 4-methylpenta-1,2,4-triene, H₂C=C=CHC(CH₃)=CH₂, H₂C=C=CH-C(CH₃)=CH₂,

Abbreviated structural formula and skeletal formula, three alkene groups, two connected in series, triene overall.

Other names applicable: 4-methyl-1,2,4-pentatriene

Number of low resolution NMR chemical shift δ signal peaks: 4 ¹H and 6 ¹³C (email if disagree?)

¹H NMR ratio of peaks: 2 : 1 : 3 : 2 (for equivalent protons)

BUT, for the 'end' =CH₂ alkene protons, you can get two chemical shifts close together, if there are two different groups attached to the other carbon of the C=C bond i.e. R"R'C=CH₂ where R" and R' are different. This causes the two =CH₂ protons to experience slightly different fields.

(19) 3-methylenepenta-1,4-diene, H₂C=CHC(=CH₂)CH=CH₂, H₂C=CH-C(=CH₂)-CH=CH₂,

Abbreviated structural formula and skeletal formula, three separated alkene groups in this triene.

Other names applicable: 3-methylene-1,4-pentadiene

Described as a conjugated compound

Number of low resolution NMR chemical shift δ signal peaks: 3 ¹H and 4 ¹³C (email if disagree?)

¹H NMR ratio of peaks: 4 (2x2) : 2 (2x1) : 2 = 2 : 1 : 1 (for equivalent protons)

BUT, for the 'end' =CH₂ alkene protons, you can get two chemical shifts close together, if there are two different groups attached to the other carbon of the C=C bond i.e. R"R'C=CH₂ where R" and R' are different. This causes the two =CH₂ protons to experience slightly different fields.

(20) cyclohexa-1,2-diene, , skeletal formula, highly strained diene.

Other names applicable: 1,2-cyclohexadene, double alkene molecule (cyclo-diene).

(20-22) are positional isomers of the alkene functional groups.

Number of low resolution NMR chemical shift δ signal peaks: 3 ¹H and 4 ¹³C (email if disagree?)

¹H NMR ratio of peaks: 2 (2x1) : 4 (2x2) : 2 = 1 : 2 :1 (for equivalent protons)

(21) cyclohexa-1,3-diene, , skeletal formula, less strained than (20)

Other names applicable: 1,2-cyclohexadene, double alkene molecule (cyclo-diene).

Number of low resolution NMR chemical shift δ signal peaks: 3 ¹H and 3 ¹³C (email if disagree?)

¹H NMR ratio of peaks: 2 (2x1) : 2 (2x1) : 4 (2x2) (for equivalent protons)

(22) cyclohexa-1,4-diene, , skeletal formula, less strained than (20)

Other names applicable: 1,4-cyclohexadene, double alkene molecule (cyclo-diene).

Number of low resolution NMR chemical shift δ signal peaks: 2 ¹H and 2 ¹³C (email if disagree?)

¹H NMR ratio of peaks: 4 (2x2) : 4 (4x1) = 1 : 1 (for equivalent protons)

(23) 1-methylcyclopenta-1,2-diene, , skeletal formula

Other names applicable: 1-methyl-1,2-cyclopentadiene.

(23-27) are positional isomers based on the two alkene groups with a diene structure based on a pentadiene ring.

Number of low resolution NMR chemical shift δ signal peaks: 4 ¹H and 6 ¹³C (email if disagree?)

¹H NMR ratio of peaks: 1 : 2 : 2 : 3 (for equivalent protons)

(24) 4-methylcyclopenta-1,2-diene, , skeletal formula

Other names applicable: 4-methyl-1,2-cyclopentadiene.

(R)-4-methylcyclpenta-1,2-diene, (R)-4-methyl-1,2-cyclopentadiene, (S)-4-methylcyclpenta-1,2-diene, (S)-4-methyl-1,2-cyclopentadiene.

Exhibits R/S stereoisomerism, the top atom of the 'pentangle' is a chiral centre.

Number of low resolution NMR chemical shift δ signal peaks: 5 ¹H and 5 ¹³C (email if disagree?)

¹H NMR ratio of peaks: 1 : 1 : 3 : 2 : 1 (for equivalent protons)

(25) 1-methylcyclopenta-1,3-diene, , skeletal formula, two separated alkene groups.

Other names applicable: 1-methyl-1,3-cyclopentadiene

Number of low resolution NMR chemical shift δ signal peaks: 5 ¹H and 6 ¹³C (email if disagree?)

¹H NMR ratio of peaks: 1 : 1 : 1 : 2 : 3 (for equivalent protons)

(26) 2-methylcyclopenta-1,3-diene, , skeletal formula, two separated alkene groups.

Other names applicable: 2-methyl-1,3-cyclopentadiene

Number of low resolution NMR chemical shift δ signal peaks: 5 ¹H and 6 ¹³C (email if disagree?)

¹H NMR ratio of peaks: 3 : 1 : 1 : 2 : 1 (for equivalent protons)

(27) 5-methylcyclopenta-1,3-diene, , skeletal formula, two separated alkene groups.

Other names applicable:  5-methyl-1,3-cyclopentadiene

Number of low resolution NMR chemical shift δ signal peaks: 4 ¹H and 4 ¹³C (email if disagree?)

¹H NMR ratio of peaks: 2 (2x1) : 2 (2x1) : 1 : 3 (for equivalent protons)

(28) 3-methylenecyclopentene, , skeletal formula

One alkene group in the ring, the other is connected by one of its carbon atoms to the ring.

Number of low resolution NMR chemical shift δ signal peaks: 5 ¹H and 6 ¹³C (email if disagree?)

¹H NMR ratio of peaks: 1 : 1 : 2 : 2 : 2 (for equivalent protons)

BUT, for the 'end' =CH₂ alkene protons, you can get two chemical shifts close together, if there are two different groups attached to the other carbon of the C=C bond i.e. R"R'C=CH₂ where R" and R' are different. This causes the two =CH₂ protons to experience slightly different fields.

(29) 4-methylenecyclopentene, , skeletal formula

One alkene group in the ring, the other is connected by one of its carbon atoms to the ring.

Number of low resolution NMR chemical shift δ signal peaks: 3 ¹H and 4 ¹³C (email if disagree?)

¹H NMR ratio of peaks: 2 (2x1) : 4 (2x2) : 2 = 1 : 2 : 1 (for equivalent protons)

(30) 1-ethylcyclobuta-1,3-diene, , skeletal formula, two separated alkene groups in the ring.

Other names applicable: 1-ethyl-1,3-cyclobutadiene, diene structure based on a butadiene ring.

Number of low resolution NMR chemical shift δ signal peaks: 5 ¹H and 6 ¹³C (email if disagree?)

¹H NMR ratio of peaks: 1 : 1 : 1 : 2 : 3 (for equivalent protons)

(31) 1,2-dimethylcyclobuta-1,3-diene, , skeletal formula, two separated alkene groups in the ring.

Other names applicable: 1,2-dimethyl-1,3-cyclobutadiene

Number of low resolution NMR chemical shift δ signal peaks: 2 ¹H and 3 ¹³C (email if disagree?)

¹H NMR ratio of peaks: 2 (2x1) : 6 (2x3) = 1 : 3 (for equivalent protons)

(32) 1,3-dimethylcyclobuta-1,3-diene, , skeletal formula, two separated alkene groups in the ring.

Other names applicable: 1,3-dimethyl-1,3-cyclbutadiene

Number of low resolution NMR chemical shift δ signal peaks: 2 ¹H and 3 ¹³C (email if disagree?)

¹H NMR ratio of peaks: 2 (2x1) : 6 (2x3) : = 1 : 3 (for equivalent protons)

(33) 1,4-dimethylcyclobuta-1,3-diene, , skeletal formula, two separated alkene groups in the ring.

Other names applicable: 1,4-dimethyl-1,3-cyclbutadiene

Number of low resolution NMR chemical shift δ signal peaks: 2 ¹H and 3 ¹³C (email if disagree?)

¹H NMR ratio of peaks: 2 (2x1) : 6 (2x3) = 1 : 3 (for equivalent protons)

(34) 1-methyl-3-methylenecyclobutene, , skeletal formula

One alkene group in the ring, the other is connected by one of its carbon atoms to the ring.

Number of low resolution NMR chemical shift δ signal peaks: 4 ¹H and 6 ¹³C (email if disagree?)

¹H NMR ratio of peaks: 3 : 2 : 2 : 1 (for equivalent protons)

BUT, for the 'end' =CH₂ alkene protons, you can get two chemical shifts close together, if there are two different groups attached to the other carbon of the C=C bond i.e. R"R'C=CH₂ where R" and R' are different. This causes the two =CH₂ protons to experience slightly different fields.

(35) 2-methyl-3-methylenecyclobutene, , skeletal formula

One alkene group in the ring, the other is connected by one of its carbon atoms to the ring.

Number of low resolution NMR chemical shift δ signal peaks: 4 ¹H and 6 ¹³C (email if disagree?)

¹H NMR ratio of peaks: 1 : 2 : 2 : 3 (for equivalent protons)

BUT, for the 'end' =CH₂ alkene protons, you can get two chemical shifts close together, if there are two different groups attached to the other carbon of the C=C bond i.e. R"R'C=CH₂ where R" and R' are different. This causes the two =CH₂ protons to experience slightly different fields.

(36) 4-methyl-3-methylenecyclobutene, , skeletal formula

One alkene group in the ring, the other is connected by one of its carbon atoms to the ring.

Exhibits R/S stereoisomerism, the top left carbon atom of the □ is a chiral centre.

Number of low resolution NMR chemical shift δ signal peaks: 5 ¹H and 6 ¹³C (email if disagree?)

¹H NMR ratio of peaks: 1 : 1 : 3 : 2 : 1 (for equivalent protons)

BUT, for the 'end' =CH₂ alkene protons, you can get two chemical shifts close together, if there are two different groups attached to the other carbon of the C=C bond i.e. R"R'C=CH₂ where R" and R' are different. This causes the two =CH₂ protons to experience slightly different fields.

(37) 3-ethylidenecyclobutene, , skeletal formula, no E/Z or R/S isomers.

One alkene group in the ring, the other is connected by one of its carbon atoms to the ring.

Number of low resolution NMR chemical shift δ signal peaks: 5 ¹H and 6 ¹³C (email if disagree?)

¹H NMR ratio of peaks: 1 : 2 : 1 : 3 : 1 (for equivalent protons)

BUT, for the 'end' =CH₂ alkene protons, you can get two chemical shifts close together, if there are two different groups attached to the other carbon of the C=C bond i.e. R"R'C=CH₂ where R" and R' are different. This causes the two =CH₂ protons to experience slightly different fields.

(38) 1-ethenylcyclobutene, , skeletal formula, no E/Z or R/S isomers.

One alkene group in the ring and the other in a side-chain.

Number of low resolution NMR chemical shift δ signal peaks: 5 ¹H and 6 ¹³C (email if disagree?)

¹H NMR ratio of peaks: 1 : 2 : 2 : 1 : 2 (for equivalent protons)

BUT, for the 'end' =CH₂ alkene protons, you can get two chemical shifts close together, if there are two different groups attached to the other carbon of the C=C bond i.e. R"R'C=CH₂ where R" and R' are different. This causes the two =CH₂ protons to experience slightly different fields.

(39) 3-ethenylcyclobutene, , skeletal formula

One alkene group in the ring and the other in a side-chain.

Exhibits R/S stereoisomerism, the top right carbon atom of the □ is a chiral centre.

(R)-3-ethenylcyclobutene, (S)-3-ethenylcyclobutene

Number of low resolution NMR chemical shift δ signal peaks: 6 ¹H and 6 ¹³C (email if disagree?)

¹H NMR ratio of peaks: 1 : 2 : 1 : 1 : 2 : 1 (for equivalent protons)

BUT, for the 'end' =CH₂ alkene protons, you can get two chemical shifts close together, if there are two different groups attached to the other carbon of the C=C bond i.e. R"R'C=CH₂ where R" and R' are different. This causes the two =CH₂ protons to experience slightly different fields.

(40) 1,2-dimethylenecyclobutane, , skeletal formula, no E/Z or R/S isomers.

Number of low resolution NMR chemical shift δ signal peaks: 2 ¹H and 3 ¹³C (email if disagree?)

¹H NMR ratio of peaks: 4 (2x2) : 4 (2x2) = 1 : 1 (for equivalent protons)

BUT, for the 'end' =CH₂ alkene protons, you can get two chemical shifts close together, if there are two different groups attached to the other carbon of the C=C bond i.e. R"R'C=CH₂ where R" and R' are different. This causes the two =CH₂ protons to experience slightly different fields.

(41) 1,3-dimethylenecyclobutane, , skeletal formula, no E/Z or R/S isomers.

Number of low resolution NMR chemical shift δ signal peaks: 2 ¹H and 3 ¹³C (email if disagree?)

¹H NMR ratio of peaks: 4 (2x2) : 4 (2x2) = 1 : 1 (for equivalent protons)

BUT, for the 'end' =CH₂ alkene protons, you can get two chemical shifts close together, if there are two different groups attached to the other carbon of the C=C bond i.e. R"R'C=CH₂ where R" and R' are different. This causes the two =CH₂ protons to experience slightly different fields.

(42) name ?, , skeletal formula

One alkene group in the ring and the other in a propene side-chain.

E/Z isomers based on the propene side chain.

CIP assignment priority rule for E/Z isomers: ₆C  >  ₁H

Number of low resolution NMR chemical shift δ signal peaks: 5 ¹H and 6 ¹³C (email if disagree?)

¹H NMR ratio of peaks: 1 : 2 : 1 : 1 : 3 (for equivalent protons)

(43) name ?, , skeletal formula, no E/Z or R/S isomers.

One alkene group in the ring and the other in a propene side-chain.

Number of low resolution NMR chemical shift δ signal peaks: 6 ¹H and 6 ¹³C (email if disagree?)

¹H NMR ratio of peaks: 1 : 2 : 2 : 1 : 2 (for equivalent protons)

BUT, for the 'end' =CH₂ alkene protons, you can get two chemical shifts close together, if there are two different groups attached to the other carbon of the C=C bond i.e. R"R'C=CH₂ where R" and R' are different. This causes the two =CH₂ protons to experience slightly different fields.

(44) name ?, , skeletal formula

One alkene group in the ring and the other in a propene side-chain.

E/Z isomers based on the propene side-chain off the ring, NOT R/S isomerism

CIP assignment priority rule for E/Z isomers: ₆C  >  ₁H

Number of low resolution NMR chemical shift δ signal peaks: 5 ¹H and 5 ¹³C (email if disagree?)

¹H NMR ratio of peaks: 2 (2x1) : 1 : 1 : 3 : 1 (for equivalent protons)

(45) name ?, , skeletal formula, no E/Z or R/S isomers.

Number of low resolution NMR chemical shift δ signal peaks: 5 ¹H and 5 ¹³C (email if disagree?)

¹H NMR ratio of peaks: 2 (2x1) : 1 : 2 : 1 : 2 (for equivalent protons)

BUT, for the 'end' =CH₂ alkene protons, you can get two chemical shifts close together, if there are two different groups attached to the other carbon of the C=C bond i.e. R"R'C=CH₂ where R" and R' are different. This causes the two =CH₂ protons to experience slightly different fields.

(46) name ?, , skeletal formula, no E/Z or R/S isomers.

Number of low resolution NMR chemical shift δ signal peaks: 4 ¹H and 6 ¹³C (email if disagree?)

¹H NMR ratio of peaks: 1 : 2 : 2 : 3 (for equivalent protons)

BUT, for the 'end' =CH₂ alkene protons, you can get two chemical shifts close together, if there are two different groups attached to the other carbon of the C=C bond i.e. R"R'C=CH₂ where R" and R' are different. This causes the two =CH₂ protons to experience slightly different fields.

(47) name ?, , skeletal formula, no E/Z or R/S isomers.

Number of low resolution NMR chemical shift δ signal peaks: 4 ¹H and 5 ¹³C (email if disagree?)

¹H NMR ratio of peaks: 2 (2x1) : 1 : 3 : 2 (for equivalent protons)

BUT, for the 'end' =CH₂ alkene protons, you can get two chemical shifts close together, if there are two different groups attached to the other carbon of the C=C bond i.e. R"R'C=CH₂ where R" and R' are different. This causes the two =CH₂ protons to experience slightly different fields.

(48) name ?, , skeletal formula, no E/Z or R/S isomers.

Number of low resolution NMR chemical shift δ signal peaks: 4 ¹H and 5 ¹³C (email if disagree?)

¹H NMR ratio of peaks: 2 (2x1) : 1 : 2 : 3 (for equivalent protons)

(49) 1,2-dimethyl-3-methylenecyclopropene, , skeletal formula, no E/Z or R/S isomers.

Number of low resolution NMR chemical shift δ signal peaks: 2 ¹H and 4 ¹³C (email if disagree?)

¹H NMR ratio of peaks: 6 (2x3) : 2 = 3 : 1 (for equivalent protons)

BUT, for the 'end' =CH₂ alkene protons, you can get two chemical shifts close together, if there are two different groups attached to the other carbon of the C=C bond i.e. R"R'C=CH₂ where R" and R' are different. This causes the two =CH₂ protons to experience slightly different fields.

(50) 3-ethylidene-1-methylcycloprop-1-ene, , skeletal formula, no E/Z or R/S isomers.

Other names applicable: 3-ethylidene-1-methylcyclopropene

Number of low resolution NMR chemical shift δ signal peaks: 4 ¹H and 6 ¹³C (email if disagree?)

¹H NMR ratio of peaks: 1 : 1 : 3 : 3 (for equivalent protons)

(51) 1-methyl-3-methylenecycloprop-1-ene, , skeletal formula, no E/Z or R/S isomers.

Other names applicable: 1-methyl-3-methylenecyclopropene

Number of low resolution NMR chemical shift δ signal peaks: 4 ¹H and 6 ¹³C (email if disagree?)

¹H NMR ratio of peaks: 1 : 2 : 2 : 3 (for equivalent protons)

BUT, for the 'end' =CH₂ alkene protons, you can get two chemical shifts close together, if there are two different groups attached to the other carbon of the C=C bond i.e. R"R'C=CH₂ where R" and R' are different. This causes the two =CH₂ protons to experience slightly different fields.

(52) 1-ethenyl-2-methylcycloprop-1-ene, , skeletal formula, no E/Z or R/S isomers.

Other names applicable: 1-ethenyl-2-methylcyclopropene

Number of low resolution NMR chemical shift δ signal peaks: 4 ¹H and 6 ¹³C (email if disagree?)

¹H NMR ratio of peaks: 3 : 2 : 1 : 2 (for equivalent protons)

BUT, for the 'end' =CH₂ alkene protons, you can get two chemical shifts close together, if there are two different groups attached to the other carbon of the C=C bond i.e. R"R'C=CH₂ where R" and R' are different. This causes the two =CH₂ protons to experience slightly different fields.

(53) 1-ethenyl-3-methylcycloprop-1-ene, , skeletal formula, no E/Z or R/S isomers.

Other names applicable: 1-ethenyl-3-methylcyclopropene

Exhibits R/S stereoisomerism, the top carbon atom of the ∆ is a chiral centre.

Number of low resolution NMR chemical shift δ signal peaks: 5 ¹H and 6 ¹³C (email if disagree?)

¹H NMR ratio of peaks: 1 : 1 : 3 : 1 : 2 (for equivalent protons)

BUT, for the 'end' =CH₂ alkene protons, you can get two chemical shifts close together, if there are two different groups attached to the other carbon of the C=C bond i.e. R"R'C=CH₂ where R" and R' are different. This causes the two =CH₂ protons to experience slightly different fields.

(54) 3-ethenyl-1-methylcycloprop-1-ene, , ?, skeletal formula

Other names applicable: 3-ethenyl-1-methylcyclopropene

Exhibits R/S stereoisomerism, the top carbon atom of the ∆ is a chiral centre.

Number of low resolution NMR chemical shift δ signal peaks: 5 ¹H and 6 ¹³C (email if disagree?)

¹H NMR ratio of peaks: 1 : 1 : 1 : 2 : 3 (for equivalent protons)

BUT, for the 'end' =CH₂ alkene protons, you can get two chemical shifts close together, if there are two different groups attached to the other carbon of the C=C bond i.e. R"R'C=CH₂ where R" and R' are different. This causes the two =CH₂ protons to experience slightly different fields.

(55) 3-ethenyl-3-methylcycloprop-1-ene, , skeletal formula

Other names applicable: 3-ethenyl-3-methylcyclopropene

Number of low resolution NMR chemical shift δ signal peaks: 4 ¹H and 5 ¹³C (email if disagree?)

¹H NMR ratio of peaks: 2 (2x1) : 3 : 1 : 2 (for equivalent protons)

BUT, for the 'end' =CH₂ alkene protons, you can get two chemical shifts close together, if there are two different groups attached to the other carbon of the C=C bond i.e. R"R'C=CH₂ where R" and R' are different. This causes the two =CH₂ protons to experience slightly different fields.

(56) 1-cyclopropylprop-2-yne, , skeletal formula

Other names applicable: 1-cyclopropyl-2-propyne.

This molecule has a saturated cycloalkane ring (cyclopropyl), but attached to an unsaturated propyne chain containing an alkyne group (triple bond C≡C).

Number of low resolution NMR chemical shift δ signal peaks: 3 ¹H and 5 ¹³C (email if disagree?)

¹H NMR ratio of peaks: 4 (2x2) : 1 : 3 (for equivalent protons)

(57) 3-cyclopropylprop-1-yne, , skeletal formula

Other names applicable: 3-cyclopropyl-1-propyne.

cyclopropyl group attached to a propyne chain - with an alkyne group.

Number of low resolution NMR chemical shift δ signal peaks: 3 ¹H and 5 ¹³C (email if disagree?)

¹H NMR ratio of peaks: 4 (2x2) : 1 : 2 : 1 (for equivalent protons)

(58) name ?, , skeletal formula

A cyclopropyl group attached to a diene chain.

Number of low resolution NMR chemical shift δ signal peaks: 3 ¹H and 5 ¹³C (email if disagree?)

¹H NMR ratio of peaks: 4 (2x2) : 1 : 3 (for equivalent protons)

(59) name ?, , skeletal formula

A bicyclo compound, one ring saturated and the other unsaturated with an alkene group.

Number of low resolution NMR chemical shift δ signal peaks: 3 ¹H and 3 ¹³C (email if disagree?)

¹H NMR ratio of peaks: 2 (2x1)  : 2 (2x1) : 4 (2x2) = 1 : 2 : 1 (for equivalent protons)

(60) Bicyclo[2.2.0]hex-1(4)-ene, , skeletal formula

A bicyclo compound, two rings connected by an alkene C=C bond which is shared by both rings..

Number of low resolution NMR chemical shift δ signal peaks: 1 ¹H and 2 ¹³C (email if disagree?)

(61) 1,1'-bi(cyclopropylidene), , skeletal formula

Other names applicable: bicyclopropylidene, cyclopropylidene-cyclopropane

A bicyclo compound, two rings connected by an alkene C=C bond.

Number of low resolution NMR chemical shift δ signal peaks: 1 ¹H and 2 ¹³C (email if disagree?)

(62) name ?, , skeletal formula

A bicyclo compound, one ring saturated and the other unsaturated with an alkene group.

Number of low resolution NMR chemical shift δ signal peaks: 6 ¹H and 6 ¹³C (email if disagree?)

¹H NMR ratio of peaks: 1 : 1 : 1 : 2 : 1 : 2 (for equivalent protons)

(63) 1-ethynyl-2-methylcyclopropane , , skeletal formula

A cycloalkane ring (cyclopropyl) and an alkyne group in a side-chain

Both E/Z isomers and R/S isomers, the bottom left and right carbon atoms of the ∆ are chiral centres (asymmetric).

(Z)-1-ethynyl-2-methylcyclopropane (cis)  a is CH₃ and b is C≡CH

and (E)-1-ethynyl-2-methylcyclopropane (trans)  a is CH₃ and b is C≡CH

This is a complicated overlap of two types of stereoisomerism - university level analysis!

Number of low resolution NMR chemical shift δ signal peaks: 5 ¹H and 6 ¹³C (email if disagree?)

¹H NMR ratio of peaks: 3 : 1 : 2 : 1 : 1 (for equivalent protons)

(64) ethynylcyclobutane, ,  skeletal formula

A cycloalkane ring (cyclobutyl) and an alkyne group in a side-chain

Number of low resolution NMR chemical shift δ signal peaks: 4 ¹H and 5 ¹³C (email if disagree?)

¹H NMR ratio of peaks: 2 : 4 (2x2) : 1 : 1 (for equivalent protons)

• 1,3‑Cyclohexadiene — a six‑membered ring containing two conjugated double bonds.

• 1,4‑Cyclohexadiene — a six‑membered ring with two isolated double bonds separated by two single bonds.

• 1,2‑Cyclohexadiene (ring‑embedded allene) — a strained isomer with cumulated double bonds inside a six‑membered ring; less stable and uncommon.

• 1‑Methylcyclopentadiene and 2‑methylcyclopentadiene — five‑membered ring systems that retain the 3 degrees of unsaturation by having two double bonds in the ring plus a methyl substituent.

• Bicyclic hexenes with one π bond and two rings (examples: bicyclo[2.2.0]hexene‑type skeletons and related strained bicyclic isomers) — one double bond plus two ring closures gives the required three degrees of unsaturation; these are typically higher in strain and reactivity.

These examples illustrate the main structural classes available for C₆H₈: cyclohexadienes (conjugated and non‑conjugated), cyclopentadiene derivatives bearing a methyl group, allenic ring systems, and bicyclic single‑double systems.

• Constitutional isomerism

  • Different connectivity of carbons and placement of double bonds produce the distinct isomers listed above (chain/ring type, position of π bonds, exocyclic versus endocyclic double bond).

• Positional isomerism

  • Double bonds can occupy different positions (1,2; 1,3; 1,4 in cyclohexadienes; 1‑ versus 2‑ methyl on cyclopentadiene), changing reactivity and spectroscopy.

• Chain (skeletal) isomerism

  • Six carbons arranged as a six‑membered ring versus a five‑membered ring plus a methyl substituent create different skeletal frameworks.

• Valence and ring‑type isomerism

  • Bicyclic isomers (two rings + one double bond) are valence/connectivity isomers of monocyclic dienes; conversion between these types may require bond reorganisation.

• Stereoisomerism and geometric isomerism

  • Where isolated double bonds exist (non‑conjugated), E/Z (cis/trans) relationships about a C=C (if substituents make them non‑equivalent) can occur. Conjugated 1,3 systems can show allylic stereochemistry in substituted derivatives.

• Conformational isomerism

  • Ring puckering and rotamers change conformations (important for cyclohexadienes and cyclopentadienes) and affect NMR and reactivity.

• Stability and enthalpy

  • Conjugated dienes (1,3‑cyclohexadiene) are thermodynamically more stable than non‑conjugated dienes (1,4‑cyclohexadiene) because of π‑electron delocalisation. Allenic ring systems (1,2‑cyclohexadiene) and highly strained bicyclic isomers have higher internal energy and are less stable.

• Boiling and melting points

  • More compact or symmetrical isomers (depending on exact structure) tend to have slightly different melting/boiling points; increased conjugation changes polarizability and can modestly alter boiling point. Strained bicyclic isomers often have higher melting points and different vapour pressures due to rigid shapes and intermolecular packing.

• Spectroscopy

  • 1H NMR: conjugated dienes show characteristic allylic and vinylic chemical shifts (vinylic protons ~4.5–6.5 ppm depending on substitution), whereas non‑conjugated dienes and allenes give distinct patterns; neopentyl‑like environments or symmetrical bicyclic systems simplify spectra.

  • IR: C=C stretches differ; conjugation lowers C=C stretching frequency relative to isolated double bonds. Allenes present unique cumulative double‑bond signatures. UV‑Vis: conjugated dienes absorb at longer wavelengths than isolated double bonds.

• Electrophilic addition

  • Isolated double bonds (1,4‑cyclohexadiene) behave like ordinary alkenes toward addition (e.g., hydrogenation, halogenation) at either double bond independently. Conjugated dienes (1,3‑cyclohexadiene) show conjugation‑controlled chemistry: they undergo 1,2‑ versus 1,4‑addition in electrophilic additions and participate in pericyclic reactions such as the Diels–Alder reaction (as dienes). Allenic systems have orthogonal π‑systems and react selectively at different termini. Bicyclic alkenes often react faster in additions because ring strain accelerates bond reorganisation.

• Diels–Alder and pericyclic chemistry

  • Conjugated dienes (1,3‑cyclohexadiene and substituted cyclopentadienes) are competent dienes in cycloadditions and form adducts selectively; non‑conjugated dienes are poor Diels–Alder partners unless isomerised or activated.

• Hydrogenation

  • Strained bicyclic isomers and isolated double bonds hydrogenate more readily than conjugated dienes due to lower resonance stabilisation in the latter. Conjugated dienes require more negative (less exothermic) hydrogenation per double bond.

• Aromatic conversion potential

  • Some C6H8 isomers (e.g., certain cyclohexadienes) are precursors to aromatic systems upon dehydrogenation; others cannot be readily aromatised without extensive bond reorganisation.

• Polymerisation and radical chemistry

  • Allenic and highly strained alkenes/bicyclics can polymerise or undergo radical opening more readily because of high ring strain and accessible radical/stabilised intermediates.

Relative reactivity summary: strained bicyclic isomers > isolated alkene isomers > conjugated dienes (most stabilized, least reactive toward simple addition) > allenic ring (reactivity depends on local geometry and substitution).

• Conjugated dienes (1,3‑systems)

  • Useful as dienes in synthetic organic chemistry (Diels–Alder partners) and as building blocks in polymer chemistry and fine chemical synthesis. Substituted cyclopentadienes are precursors to cyclopentadienyl ligands in organometallic chemistry.

• Non‑conjugated dienes and monocyclic alkenes

  • Serve as intermediates in organic synthesis where selective functionalisation of one double bond is required; hydrogenation/halogenation patterns can be exploited in multi‑step syntheses.

• Allenic and strained bicyclic isomers

  • Primarily research compounds and specialised synthons; exploited in mechanistic studies, strained‑ring chemistry, or in designing reactions that release strain energy (synthetic transforms, ring‑opening polymerizations).

Practical note: many simple C₆H₈ isomers are mainly useful as synthetic intermediates or teaching examples rather than bulk industrial commodities.

• “All isomers with same formula have similar reactivity” — false: connectivity, conjugation and strain dominate reactivity.

• “Conjugated dienes always react faster than isolated alkenes” — false: conjugated dienes are stabilised and often less reactive toward simple electrophilic addition than isolated alkenes, but they participate in pericyclic reactions that isolated alkenes do not.

• “All double bonds behave identically in a ring” — false: position, conjugation, and ring strain change regiochemistry, stereochemistry and rates.

• “All C6H8 isomers are easy to interconvert” — false: many interconversions require high energy (thermally or photochemically driven) and may be irreversible or require catalysts.

• Confusion between resonance structures and distinct constitutional isomers — emphasise that distinct isomers are isolable molecules with different energies, not resonance contributors.

• Learn to classify C6H8 isomers by their skeletal type: cyclohexadiene (conjugated versus non‑conjugated), cyclopentadiene derivatives, allenic ring, and bicyclic single‑double systems. Sketch one clear example from each class.

• When asked to compare reactivity, always state the structural reason in one line: e.g., “1,3‑cyclohexadiene reacts by Diels–Alder because its conjugated π system supplies a 4π electron component, and conjugation lowers reactivity in simple electrophilic addition.”

• Practice predicting major products for electrophilic addition to conjugated versus isolated dienes (1,2 versus 1,4 addition) and draw mechanism arrows showing resonance‑stabilised carbocations for conjugated systems.

• Remember spectral signatures: vinylic protons in 1H NMR, allylic shifts, and IR C=C frequency shifts on conjugation; use these clues in identification questions.

• For mechanistic questions, explicitly name the controlling principle (resonance stabilisation, ring strain, steric hindrance, orbital symmetry in pericyclic reactions). Keep answers compact and evidence‑based.

• In timed exams, use a small comparison table: isomer → key structural feature → expected reactivity difference (one‑line each). This is concise and marks‑friendly.

• Practice a few past paper questions on dienes and pericyclic chemistry for each exam board listed; emphasise mechanism diagrams and clear statements about thermodynamic versus kinetic control.

Does C6H8 have any stereoisomers?

The molecular structure and naming of ALKENES (how to name and draw alkene structures)

Index of revision notes on the chemistry of ALKANES and the petrochemical industry