mass spectrum of 1-iodobutane C4H9I CH3CH2CH2CH2I fragmentation pattern of m/z m/e ions for analysis and identification of 1-iodobutane image diagram doc brown's advanced organic chemistry revision notes

Advanced Organic Chemistry: Mass spectrum of 1-iodobutane (butyl iodide) CH₃CH₂CH₂CH₂I

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Interpreting and explaining the mass spectrum of 1-iodobutane (butyl iodide)

[Author © Dr Phil Brown GRIC, PhD: Doc Brown's advanced level organic chemistry exam revision notes suitable for students of UK A level chemistry courses & US K12 grade 11, grade 12 and AP honors chemistry courses: Molecular spectroscopy analysis of 1-iodobutane (mass spectra) [spectra page updated RE-EDIT]

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and Isomers of molecular formula C₄H₉X (where X = F, Cl, Br or I and basic data on NMR chemical shifts)

Practise exam questions based on the mass spectrum of 1-iodobutane

Introductory note on the mass spectrum of 1-iodobutane

Students and teachers please note my explanation of the mass spectrum of 1-iodobutane is designed for advanced, but pre-university, chemistry courses.

If M represents the 1-iodobutane molecule, the initial ionisation to give the molecular ion is:

M_(g) + high KE e^- ==> [M•]⁺_(g) + 2e^- and fragmentation equations assume [M]⁺ is the start of the processes and all species are in a gaseous state.

I've not usually shown an unpaired electron on e.g. an ion or a non-ionised alkyl radical R e.g.

[M•]⁺ ==> [X]⁺ + R•, but you should be aware this is a more accurate depiction of some processes.

I've used simplified equations to show how some of the ions might be formed in the fragmentation pattern for 1-iodobutane.

I've included stick diagram and table of m/z ions for the mass spectrum of 1-iodobutane and conducting the mass spectrum analysis under standard conditions, a database can be built up based complex fingerprint patterns, often involving relative intensities of many fragment ions, that can be used to identify compounds including 1-iodobutane.

In selected cases, where two different fragment ions have the same integer m/z value, I've pointed out that modern mass spectrometers can measure relative ion mass to four decimal places. So, using accurate isotopic masses, I've calculated and compared the accurate ion masses if appropriate for 2-iodobutane. BUT strictly speaking, 0.0005 should be deducted for singly charged ions to account for the loss of the electron in their formation. I have NOT done this for 2-iodobutane, but the mass spectrometer software does!

mass spectrum of 1-iodobutane C4H9I CH3CH2CH2CH2I fragmentation pattern of m/z m/e ions for analysis and identification of 1-iodobutane image diagram doc brown's advanced organic chemistry revision notes

1-iodobutane, (n-butyl iodide), C₄H₉I, CH₃-CH₂-CH₂-CH₂-I

The molecular structure and naming of haloalkanes

Interpreting the fragmentation pattern of the mass spectrum of 1-iodobutane

[M]⁺ is the parent molecular ion peak (M) with an m/z of 184 corresponding to [C₄H₉I]⁺, the original 1-iodobutane molecule minus an electron, [CH₃CH₂CH₂CH₂I]⁺

Iodine consists of 100% of the ¹²⁷I isotope, so there are no double peak complexities with 1-iodobutane that you get with the mass spectra of organic chlorine and bromine compounds, where you get M+2 peaks due to two isotopes of the halogen of mass difference 2 units and other double peaks two m/z units apart.

See Mass spectroscopy index

Unless otherwise stated, C means a ¹²C atom, if not, the isotopic carbon atom ¹³C will be indicated.

The small M+1 peak at m/z 185, corresponds to an ionised 1-iodobutane molecule with one ¹³C atom in it i.e. an ionised 1-iodobutane molecule of formula [¹³C¹²C₃H₉I]⁺

Carbon-13 only accounts for ~1% of all carbon atoms (¹²C ~99%), but the more carbon atoms in the molecule, the greater the probability of observing this ¹³C M+1 peak.

1-iodobutane has 4 carbon atoms, so on average, ~1 in 25 molecules will contain a ¹³C atom, though the M+1 peak doesn't seem to reflect this..

You may find two peaks one unit apart with a height ratio of 25:1 e.g. m/z ions 57/58 and 184/185.

The most abundant ion of the molecule under mass spectrometry investigation (1-iodobutane) is usually given an arbitrary abundance value of 100, called the base ion peak, and all other abundances ('intensities') are measured against it.

The base ion peak for the mass spectrum of 1-iodobutane is the m/z 57 ion [C₄H₉]⁺

Identifying the species giving the most prominent peaks (apart from M) in the fragmentation pattern of 1-iodobutane.

Unless otherwise indicated, assume the carbon atoms in 1-iodobutane are the ¹²C isotope.

Some of the possible positive ions, [molecular fragment]⁺, formed in the mass spectrometry of 1-iodobutane.

The parent molecular ion of 1-iodobutane m/z 184: [CH₃CH₂CH₂CH₂I]⁺

Data table of some of the ions formed in the fragmentation pattern of the mass spectrum of 1-iodobutane

m/z value of [fragment]⁺	185	184	155	141	128	127	58
[molecular fragment]⁺	[¹³C¹²C₃H₉I]⁺	[C₄H₉I]⁺	[C₂H₄I]⁺	[CH₂I]⁺	[HI]⁺	[I]⁺	[¹³C¹²C₃H₉]⁺

m/z value of [fragment]⁺	57	55	41	39	29	28	27
[molecular fragment]⁺	[C₄H₉]⁺	[C₄H₇]⁺	[C₃H₅]⁺	[C₃H₃]⁺	[C₂H₅]⁺	[C₂H₄]⁺	[C₂H₃]⁺

Analysing and explaining the principal ions in the fragmentation pattern of the mass spectrum of 1-iodobutane

PLEASE NOTE I have found it difficult to find 'authentic' equations to explain mass spectra fragmentation patterns and it is complex chemistry! I've identified the formulae of the ionised fragments on the mass spectrum diagram, but the equations are from the internet or my conjecture as to how the ions might be formed - please take care in using the information, especially for assignments at university or pre-university level.

Atomic masses: H = 1; C = 12; I = 127

Bond enthalpies = kJ/mol: C-C = 348; C-H = 412; C-I = 238

Possible equations to explain some of the most abundant ion peaks of 1-iodobutane (tabulated above)

Formation of m/z 155 ion:

[CH₃CH₂CH₂CH₂I]⁺ ===> [C₂H₄I]⁺ + C₂H₅

C-C bond scission in the parent molecular ion,

mass change 184 - 29 = 155 (M-29 ion peak)

Low probability of formation due to large bond enthalpy (compared to C-I bond enthalpy.

Note that iodine has one stable isotope, so no double peak complications you get with organo-chlorine or organo-bromine compounds.

Formation of m/z 141 ion:

[CH₃CH₂CH₂CH₂I]⁺ ===> [CH₂I]⁺ + C₃H₇

C-C bond scission in the parent molecular ion,

mass change 184 - 43 = 141 (M-43 ion peak)

Low probability of formation due to large bond enthalpy (compared to C-I bond enthalpy).

Formation of m/z 127 and 128 ions:

[CH₃CH₂CH₂CH₂I]⁺ ===> [I]⁺ + C₄H₉

C-I bond scission, iodine atom becomes ionised,

mass change 184 - 57 = 127 (M-57 ion peak)

The m/z of 127 is indicative of an iodine compound.

[CH₃CH₂CH₂CH₂I]⁺ ===> [HI]⁺ + C₄H₈

Elimination of a hydrogen iodide molecule, mass change 184 - 56 = 128.

Both reactions have a low probability judging from the small abundances - small peaks.

Formation of m/z 57 ion:

[CH₃CH₂CH₂CH₂I]⁺ ===> [C₄H₉]⁺ + I

Scission of the weakest bond in the molecule, breakage of the C-I bond releases an iodine atom and forms the base peak ion of the butyl ion.

The alkyl carbocation is much more likely to carry the positive charge than the iodine atom.

The [C₄H₉]⁺ ion is likely to be the more stable secondary carbocation [(CH₃)₃C]⁺ rather than the linear butyl carbocation [CH₃CH₂CH₂CH₂]⁺.

The m/z 57 ion is the base peak ion, the most abundant and 'stable' ion fragment.

The m/z 58 ion is probably, [¹³C¹²C₃H₉]⁺, i.e. the base peak ion containing a ¹³C isotope.

Formation of m/z 55 ion:

[C₄H₉]⁺ ===> [C₄H₇]⁺ + H₂

Elimination of hydrogen from the m/z 57 ion.

Loss of a H atom from the same ion can also form the m/z 55 ion.

Low probability for these fragmentation reactions due to the high C-H bond enthalpy.

Formation of m/z 41 and 39 ions:

Possible reactions include:

m/z 41: [C₄H₈]⁺ ===> [C₃H₅]⁺ + CH₃

m/z 39: [C₃H₅]⁺ ===> [C₃H₃]⁺ + H₂

Formation of m/z 29, 28 and 27 ions:

Possible reactions include:

m/z 29: [CH₃CH₂CH₂CH₂I]⁺ ===> [CH₃CH₂]⁺ + CH₂CH₂I

From bond scission in the parent molecular ion (above) or C-C bond scission of the fragmentation ions - all sorts of possibilities.

m/z 27: [C₄H₈]⁺ ===> [C₂H₃]⁺ + C₂H₅

m/z 28: [C₄H₈]⁺ ===> [C₂H₄]⁺ + C₂H₄

m/z 28: [C₄H₉]⁺ ===> [C₂H₄]⁺ + C₂H₅

m/z 29: [C₄H₈]⁺ ===> [C₂H₅]⁺ + C₂H₃

m/z 29: [C₄H₉]⁺ ===> [C₂H₅]⁺ + C₂H₄

QUESTIONS

Advanced A-level chemistry - practise exam questions on the mass spectrum of 1-iodobutane

This is a joint AI-doc b experiment!

Jot down your responses and check out the answers: ANSWERS

If you think there are any errors, please email me asap at chem55555@hotmail.com

I don't mind if students/teachers do a selected printout of these questions and answers.

Q1. The mass spectrum of 1‑iodobutane shows a strong peak at $m / z = 127$ . What is this peak?

A. $C 4 H 9 +$ B. $I +$ C. $C 3 H 7 +$ D. $C 2 H 5 I +$

Q2. Which feature in the mass spectrum of 1-iodobutane is most characteristic of iodine?

A. A 1:1 doublet separated by 2 m/z units

B. A 3:1 doublet separated by 2 m/z units

C. A single dominant peak at $m / z = 127$

D. A cluster of peaks around $m / z = 80$

Q3. The molecular formula of 1‑iodobutane is $C 4 H 9 I$ . The molecular ion peak appears at approximately:

A. $m / z = 137$ B. $m / z = 155$ C. $m / z = 184$ D. $m / z = 127$

Q4. A strong peak at $m / z = 43$ is commonly observed in the mass spectrum of 1‑iodobutane. Which fragment does this correspond to?

A. $C 3 H 7 +$ B. $C 2 H 5 +$ C. $I +$ D. $C 4 H 9 +$

Q5. Why does the molecular ion peak of 1‑iodobutane appear as a single peak, not a doublet like brominated or chlorinated compounds?

A. Iodine has only one stable isotope

B. Iodine isotopes have identical masses

C. Iodine isotopes differ by 1 m/z unit

D. Iodine isotopes differ by 2 m/z units

Q6. Which statement best explains the intensity of the $m / z = 127$ peak in the mass spectrum of 1‑iodobutane?

A. $I +$ is a relatively stable cation

B. $I +$ is formed by rearrangement of the carbon chain

C. $I +$ is produced only at high resolution

D. $I +$ forms only when the molecular ion is absent

Q7. Which fragment is responsible for a peak at $m / z = 57$ in the mass spectrum of 1‑iodobutane?

A. $C 2 H 5 +$ B. $C 3 H 5 +$ C. $C 3 H 7 +$ D. $C 4 H 9 +$

Correct answer: D

Q8. A student claims: “The base peak must always be the halogen ion.” Why is this incorrect for 1‑iodobutane?

A. The halogen ion is never formed

B. The base peak is the highest m/z peak

C. Hydrocarbon cations can be more stable than the molecular ion

D. The base peak always corresponds to the molecular ion

Q9. Distinguishing iodinated from brominated compounds

Which observation confirms that the compound is iodinated, not brominated?

A. A single peak at $m / z = 127$

B. A doublet at $m / z = 79$ and 81

C. A doublet at $m / z = 137$ and 139

D. A 3:1 doublet at $m / z = 127$ and 129

Q10. A spectrum shows:

A molecular ion at $m / z = 184$
A very strong peak at $m / z = 127$
A strong peak at $m / z = 43$

Which conclusion is most reasonable?

A. The compound is 1‑chlorobutane

B. The compound is 1‑iodobutane

C. The compound is an unhalogenated alkane

D. The compound is an alcohol

Jot down your responses and check out the answers: ANSWERS

If you think there are any errors, please email me asap at chem55555@hotmail.com

Comparing the infrared, mass, 1H NMR and 13C NMR spectra of the 4 halogenoalkane isomers of C₄H₉I NOTE: The images are linked to their original detailed spectral analysis pages AND can be doubled in size with touch screens to increase the definition to the original 1-iodobutane, 2-iodobutane, 1-iodo-2-methylpropane and 2-iodo-2-methylpropane image sizes. These four molecules are structural isomers of molecular formula C₄H₉I and exemplify the infrared, mass, 1H NMR and 13C NMR spectra of lower aliphatic halogenoalkanes (haloalkanes, alkyl halides, iodoalkanes, alkyl iodides).


INFRARED SPECTRA (above): Apart from the significant differences in the fingerprint region at wavenumbers 1500 to 400 cm^-1, there are no other great striking differences, but each could be identified from its infrared spectrum.


MASS SPECTRA (above): All four give the parent molecular ion of m/z 184, but it is only a relatively tiny peak for 2-iodo-2-methylpropane. All four give the base ion peak of m/z 57. All four give prominent peaks for m/z ions 29 and 41 and all give a tiny peak from an ionised iodine atom at m/z 127. They look quite similar to me and lack a clear fingerprint fragmentation pattern.


1H NMR SPECTRA (above): The 1H NMR spectra of all three molecules give different proton ratios i.e.1-iodobutane four peaks 3:2:2:2, 2-iodobutane four peaks 3:3:2:1, 1-iodo-2-methylpropane three peaks 6:2:1 and 2-iodo-2-methylpropane one peak '1' (effectively no ratio involved), so all four molecular structures can be distinguished from each other by their ¹H NMR spectra proton ratios, numbers of peaks and (n+1) rule splitting patterns.


13C NMR SPECTRA (above): The 13C NMR spectra of the four molecules show various numbers of carbon-13 chemical environments i.e 1-iodobutane and 2-iodobutane show four 13C NMR resonances, 1-iodo-2-methylpropane three 13C NMR resonances and 2-iodo-2-methylpropane only two 13C resonances. Therefore 1-iodo-2-methylpropane and 2-iodo-2-methylpropane can be distinguished from the other three by their number of resonances in their 13C NMR spectra, but 1-iodobutane and 2-iodobutane cannot be distinguished from each other from their number of 13C NMR resonance lines - other data would be required.

Key words & phrases: isomer of molecular formula C4H9I CH3CH2CH2CH2I image diagram on how to interpret and explain the mass spectrum of 1-iodobutane m/z m/e base peaks, image and diagram of the mass spectrum of 1-iodobutane, details of the mass spectroscopy of 1-iodobutane, low and high resolution mass spectrum of 1-iodobutane, prominent m/z peaks in the mass spectrum of 1-iodobutane, comparative mass spectra of 1-iodobutane, the molecular ion peak in the mass spectrum of 1-iodobutane, analysing and understanding the fragmentation pattern of the mass spectrum of 1-iodobutane, characteristic pattern of peaks in the mass spectrum of 1-iodobutane, relative abundance of mass ion peaks in the mass spectrum of 1-iodobutane, revising the mass spectrum of 1-iodobutane, revision of mass spectroscopy of 1-iodobutane, most abundant ions in the mass spectrum of 1-iodobutane, how to construct the mass spectrum diagram for abundance of fragmentation ions in the mass spectrum of 1-iodobutane, how to analyse the mass spectrum of 1-iodobutane, how to describe explain the formation of fragmented ions in the mass spectra of 1-iodobutane equations for explaining the formation of the positive ions in the fragmentation of the ionised molecule of 1-iodobutane recognising the base ion peak of 1-iodobutane interpreting interpretation the mass spectrum of 1-iodobutane functional group haloalkane halogenoalkane alkyl bromide n-butyl iodide Stick diagram of the relative abundance of ionised fragments in the fingerprint pattern of the mass spectrum of 1-iodobutane. Table of the m/e m/z values and formula of the ionised fragments in the mass spectrum of 1-iodobutane. The m/e m/z value of the molecular ion peak in the mass spectrum of 1-iodobutane. The m/e m/z value of the base ion peak in the mass spectrum of 1-iodobutane. Possible examples of equations showing the formation of the ionised fragments in 1-iodobutane. Revision notes on the mass spectrum of 1-iodobutane. Matching and deducing the structure of the 1-iodobutane molecule from its mass spectrum. Mass spectroscopy of aliphatic halogenoalkanes iodoalkanes, mass spectra of 1-iodobutane, an isomer of molecular formula C4H9I How do you interpret the mass spectrum of 1-iodobutane How to interpret the mass spectrum of 1-iodobutane Explanatory diagram of the mass spectrum of the 1-iodobutane molecule in terms of its molecular structure. Table listing data of the m/z ion prominent main peaks in the mass spectrum of 1-iodobutane. How to explain the mass spectrum of 1-iodobutane. The m/z value of the molecular ion peak in the mass spectrum of 1-iodobutane. Identifying 1-iodobutane from its mass spectrum pattern. The m/z m/e peak analysis interpretation diagram of the mass spectrum of the 1-iodobutane molecule. The uses of the mass spectrum of the 1-iodobutane molecule. The distinctive features of the mass spectrum of the 1-iodobutane molecule explained. explaining the fragmentation pattern of the mass spectrum of 1-iodobutane equations showing the formation of the ionised fragments in the mass spectrum of 1-iodobutane what does the mass spectrum tell you about the structure and properties of the 1-iodobutane molecule? Data table of ionised fragments in the mass spectrum of 1-iodobutane and equations for their formation in the fragmentation of the ionised 1-iodobutane molecule.

Links associated with 1-iodobutane

The chemistry of HALOGENOALKANES (haloalkanes) revision notes INDEX

The infrared spectrum of 1-iodobutane (n-butyl iodide)

The H-1 NMR spectrum of 1-iodobutane (n-butyl iodide)

The C-13 NMR spectrum of 1-iodobutane (n-butyl iodide)

Mass spectrometry index

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ANSWERS

Advanced A-level chemistry - practise exam questions on the mass spectrum of 1-iodobutane

If you think there are any errors, please email me asap at chem55555@hotmail.com

I don't mind if students/teachers do a selected printout of these questions and answers.

Q1. The mass spectrum of 1‑iodobutane shows a strong peak at $m / z = 127$ . What is this peak?

A. $C 4 H 9 +$ B. $I +$ C. $C 3 H 7 +$ D. $C 2 H 5 I +$

Correct answer: B

Explanation:

Iodine has one major stable isotope, ¹²⁷I.
The strong peak at $m / z = 127$ corresponds to the iodine cation, $I +$ .
This is a very characteristic feature of iodinated compounds.

Common misconception:

Choosing A or C: assuming hydrocarbon fragments always dominate.
Choosing D: overcomplicating and assuming a larger iodinated fragment rather than the simple halogen ion.

Q2. Which feature in the mass spectrum of 1-iodobutane is most characteristic of iodine?

A. A 1:1 doublet separated by 2 m/z units

B. A 3:1 doublet separated by 2 m/z units

C. A single dominant peak at $m / z = 127$

D. A cluster of peaks around $m / z = 80$

Correct answer: C

Explanation:

Iodine has essentially one abundant isotope, ¹²⁷I.
This gives a single strong peak at $m / z = 127$ , rather than a doublet.
Bromine and chlorine show characteristic doublets (1:1 for Br, 3:1 for Cl).

Common misconception:

Choosing A or B: confusing iodine with bromine or chlorine isotopic patterns.
Choosing D: thinking any cluster near 80 must be iodine.

Q3. The molecular formula of 1‑iodobutane is $C 4 H 9 I$ . The molecular ion peak appears at approximately:

A. $m / z = 137$ B. $m / z = 155$ C. $m / z = 184$ D. $m / z = 127$

Correct answer: C

Explanation:

Calculate the nominal mass:

(4 \times 12) +(9 \times 1) + 127 = 48 + 9 + 127 = 184

So the molecular ion appears at $m / z \approx 184$ .
$m / z = 127$ is the iodine fragment, not the molecular ion.

Common misconception:

Choosing D: confusing the strong $I +$ peak with the molecular ion.
Choosing 137 or 155: random guessing without using the formula.

Q4. A strong peak at $m / z = 43$ is commonly observed in the mass spectrum of 1‑iodobutane. Which fragment does this correspond to?

A. $C 3 H 7 +$ B. $C 2 H 5 +$ C. $I +$ D. $C 4 H 9 +$

Correct answer: A

Explanation:

$m / z = 43$ corresponds to the propyl cation, $C 3 H 7 +$ .
This is a stable carbocation fragment formed from the butyl chain and often becomes a strong or base peak.

Common misconception:

Choosing C: assuming the halogen fragment is always the strongest peak.
Choosing D: thinking the whole butyl cation dominates rather than the more stable propyl cation.

Q5. Why does the molecular ion peak of 1‑iodobutane appear as a single peak, not a doublet like brominated or chlorinated compounds?

A. Iodine has only one stable isotope

B. Iodine isotopes have identical masses

C. Iodine isotopes differ by 1 m/z unit

D. Iodine isotopes differ by 2 m/z units

Correct answer: A

Explanation:

Iodine is dominated by a single stable isotope, ¹²⁷I.
Therefore, the molecular ion appears as one peak at $m / z = 184$ , with no visible isotopic splitting.

Common misconception:

Assuming iodine behaves like Cl or Br with visible doublets.
Choosing B: misunderstanding isotopes—different isotopes cannot have identical masses.

Q6. Which statement best explains the intensity of the $m / z = 127$ peak in the mass spectrum of 1‑iodobutane?

A. $I +$ is a relatively stable cation

B. $I +$ is formed by rearrangement of the carbon chain

C. $I +$ is produced only at high resolution

D. $I +$ forms only when the molecular ion is absent

Correct answer: A

Explanation:

The C-I bond can cleave to give a stable iodine cation, $I +$
This stability leads to a strong peak at $m / z = 127$ .
Note that the C-I bond enthalpy is much less than the C-C or C-H bond enthalpies.

Common misconception:

Choosing B: thinking the intensity is due to complex rearrangements rather than simple bond cleavage.
Choosing D: assuming $I +$ only appears when the molecular ion is missing.

Q7. Which fragment is responsible for a peak at $m / z = 57$ in the mass spectrum of 1‑iodobutane?

A. $C 2 H 5 +$ B. $C 3 H 5 +$ C. $C 3 H 7 +$ D. $C 4 H 9 +$

Correct answer: D

Explanation:

m / z = 57

corresponds to the butyl cation,

C 4 H 9 +

This is another common hydrocarbon fragment from the butyl chain.

Common misconception:

Confusing 57 with 43 (propyl cation) and choosing C.

Q8. A student claims: “The base peak must always be the halogen ion.” Why is this incorrect for 1‑iodobutane?

A. The halogen ion is never formed

B. The base peak is the highest m/z peak

C. Hydrocarbon cations can be more stable than the molecular ion

D. The base peak always corresponds to the molecular ion

Correct answer: C

Explanation:

The base peak is the most intense peak, not necessarily the halogen ion.
In many spectra, stable hydrocarbon cations (e.g. $C 3 H 7 +$ at 43) can be more abundant than $molecular ion$ .

Common misconception:

Assuming halogen ions dominate all spectra.
Confusing “base peak” with “highest m/z” or “molecular ion”.

Q9. Distinguishing iodinated from brominated compounds

Which observation confirms that the compound is iodinated, not brominated?

A. A single peak at $m / z = 127$

B. A doublet at $m / z = 79$ and 81

C. A doublet at $m / z = 137$ and 139

D. A 3:1 doublet at $m / z = 127$ and 129

Correct answer: A

Explanation:

A single strong peak at 127 indicates iodine (¹²⁷I).
Bromine would show 1:1 doublets at 79/81 or 137/139.
Chlorine would show a 3:1 doublet at appropriate m/z values.

Common misconception:

Choosing B or C: confusing iodine with bromine’s doublet patterns.
Choosing D: inventing a chlorine-like pattern at the wrong m/z.

Q10. A spectrum shows:

A molecular ion at $m / z = 184$
A very strong peak at $m / z = 127$
A strong peak at $m / z = 43$

Which conclusion is most reasonable?

A. The compound is 1‑chlorobutane

B. The compound is 1‑iodobutane

C. The compound is an unhalogenated alkane

D. The compound is an alcohol

Correct answer: B

Explanation:

Molecular ion at 184 → matches $C 4 H 9 I$ .
Strong $I +$ peak at 127 → iodine present.
Strong hydrocarbon fragment at 43 → propyl cation from the butyl chain.
Together, these features are consistent with 1‑iodobutane.

Common misconception:

Choosing A: expecting chlorine but there is no 3:1 doublet.
Choosing C or D: ignoring the clear iodine fragment and molecular ion mass.

Q1. The mass spectrum of 1‑iodobutane shows a strong peak at m/z=127. What is this peak?

Q2. Which feature in the mass spectrum of 1-iodobutane is most characteristic of iodine?

Q3. The molecular formula of 1‑iodobutane is C4H9I. The molecular ion peak appears at approximately:

Q4. A strong peak at m/z=43 is commonly observed in the mass spectrum of 1‑iodobutane. Which fragment does this correspond to?

Q5. Why does the molecular ion peak of 1‑iodobutane appear as a single peak, not a doublet like brominated or chlorinated compounds?

Q6. Which statement best explains the intensity of the m/z=127 peak in the mass spectrum of 1‑iodobutane?

Q7. Which fragment is responsible for a peak at m/z=57 in the mass spectrum of 1‑iodobutane?

Q8. A student claims: “The base peak must always be the halogen ion.” Why is this incorrect for 1‑iodobutane?

Q9. Distinguishing iodinated from brominated compounds

Q10. A spectrum shows:

Q1. The mass spectrum of 1‑iodobutane shows a strong peak at m/z=127. What is this peak?

Q2. Which feature in the mass spectrum of 1-iodobutane is most characteristic of iodine?

Q3. The molecular formula of 1‑iodobutane is C4H9I. The molecular ion peak appears at approximately:

Q4. A strong peak at m/z=43 is commonly observed in the mass spectrum of 1‑iodobutane. Which fragment does this correspond to?

Q5. Why does the molecular ion peak of 1‑iodobutane appear as a single peak, not a doublet like brominated or chlorinated compounds?

Q6. Which statement best explains the intensity of the m/z=127 peak in the mass spectrum of 1‑iodobutane?

Q7. Which fragment is responsible for a peak at m/z=57 in the mass spectrum of 1‑iodobutane?

Q8. A student claims: “The base peak must always be the halogen ion.” Why is this incorrect for 1‑iodobutane?

Q9. Distinguishing iodinated from brominated compounds

Q10. A spectrum shows:

Q1. The mass spectrum of 1‑iodobutane shows a strong peak at $m / z = 127$ . What is this peak?

Q3. The molecular formula of 1‑iodobutane is $C 4 H 9 I$ . The molecular ion peak appears at approximately:

Q4. A strong peak at $m / z = 43$ is commonly observed in the mass spectrum of 1‑iodobutane. Which fragment does this correspond to?

Q6. Which statement best explains the intensity of the $m / z = 127$ peak in the mass spectrum of 1‑iodobutane?

Q7. Which fragment is responsible for a peak at $m / z = 57$ in the mass spectrum of 1‑iodobutane?

Q1. The mass spectrum of 1‑iodobutane shows a strong peak at $m / z = 127$ . What is this peak?

Q3. The molecular formula of 1‑iodobutane is $C 4 H 9 I$ . The molecular ion peak appears at approximately:

Q4. A strong peak at $m / z = 43$ is commonly observed in the mass spectrum of 1‑iodobutane. Which fragment does this correspond to?

Q6. Which statement best explains the intensity of the $m / z = 127$ peak in the mass spectrum of 1‑iodobutane?

Q7. Which fragment is responsible for a peak at $m / z = 57$ in the mass spectrum of 1‑iodobutane?