Advanced Organic Chemistry: 1H NMR spectrum of bromomethane

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The H-1 hydrogen-1 (proton) NMR spectrum of bromomethane (methyl bromide)

Doc Brown's Chemistry Advanced Level Pre-University Chemistry Revision Study Notes for UK IB KS5 A/AS GCE advanced A level organic chemistry students US K12 grade 11 grade 12 organic chemistry courses involving molecular spectroscopy analysing H-1 NMR spectra of bromomethane

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H-1 proton NMR spectroscopy - spectra index

CH3Br low and high resolution 1H proton nmr spectrum of bromomethane analysis interpretation of chemical shifts ppm spin spin line splitting diagram H1 H-1 nmr for methyl bromide explaining spin-spin coupling for line splitting doc brown's advanced organic chemistry revision notes

TMS is the acronym for tetramethylsilane, formula Si(CH3)4, whose protons are arbitrarily given a chemical shift of 0.0 ppm. This is the 'standard' in 1H NMR spectroscopy and all other proton resonances, called chemical shifts, are measured with respect to the TMS, and depend on the individual (electronic) chemical environment of the hydrogen atoms in an organic molecule - bromomethane here.

The chemical shifts quoted in ppm on the diagram of the H-1 NMR spectrum of bromomethane represent the peaks of the intensity of the chemical shifts of (which are often groups of split lines at high resolution) AND the relative integrated areas under the peaks gives you the ratio of protons in the different chemical environments of the bromomethane molecule.

Bromomethane, CH3Br (methyl bromide)

Interpreting the H-1 NMR spectrum of bromomethane

There is only one 1H chemical shift observed, because there is only one protonated carbon atom attached to three equivalent hydrogen atoms - which cannot split each other, so all you see in the 1H NMR spectrum of bromomethane is a single singlet resonance.

Comparing the 1H NMR chemical shift of bromomethane with other halogen compounds

(1) Comparing monosubstituted halogen derivatives of methane

Comparing the effect of a mono-substituent in the methane molecule

Compound fluoromethane chloromethane bromomethane iodomethane methane
Formula CH3F CH3Cl CH3Br CH3I CH4
1H chemical shift/ppm 4.1 3.05 2.68 2.16 0.23
Pauling electronegativity F   4.0 Cl   3.0 Br   2.8 I   2.5 H   2.1

With the increase in electronegativity of the halogen, the 1H chemical shift for these molecules steadily increases.

(2) Comparing the effects of increasing chlorine substitution of methane

Comparing the effect of polysubstitution of methane with chlorine.

Compound methane chloromethane dichloromethane trichloromethane tetrachloromethane
Formula CH4 CH3Cl CH2Cl2 CHCl3 CCl4
1H chemical shift/ppm 0.23 3.05 5.30 7.27 not applicable

With increase in chlorine substitution, the 1H NMR chemical shift is increased.

Increasing the number of atoms more electronegative than carbon or hydrogen, increases the 1H NMR chemical shift.

You would expect a similar trend for the equivalent bromine compounds.

Number of directly adjacent protons 1H causing splitting Splitting pattern produced from the n+1 rule on spin-spin coupling and the theoretical ratio of line intensities
0 means no splitting             1            
1 creates a doublet           1   1          
2 creates a triplet         1   2   1        
3 creates a quartet       1   3   3   1      
4 creates a quintet     1   4   6   4   1    
5 creates a sextet   1   5   10   10   5   1  
6 creates a septet 1   6   15   20   15   6   1

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Links associated with bromomethane

The chemistry of HALOGENOALKANES (haloalkanes) revision notes INDEX

H-1 proton NMR spectroscopy index  (Please read 8 points at the top of the 1H NMR index page)


All Advanced Organic Chemistry Notes

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