Question

Interpret the 1H NMR and 13C NMR spectra data provided as evidence of the structure of styrene.

Styrene H-NMR Styrene C-NMR Styrene in CDC13 VI 135 130 125 120 ppm 200 190 180 170 160 50 140 130 120 110 100 90 80 70 60 50 4030 20 10 ppm

Answer 1

In the given 1H-nmr spectrum of styrene or phenyl ehtene, the main peaks are written as :

1. due to presence of double bond here cis- and trans-Hs are present which gives different chemical shift values (geminal protons/diastereotopic protons).

2. In this vinyl system, benzene attached proton showed doublet of doublet due to presence of geminal hydrogens, A gives doublet and this further split by M proton therefore 4 lines of similar intensity are observed at delta 6.76 ppm.

3. The resonance of M proton is split as a doublet of doublet (dd) at around delta 5.4, due to coupling with geminal H as well as Cis- H present near by C.

4. The resonance of A proton is split as a doublet of doublet (dd) at around delta 5.7, due to coupling with geminal H as well as trans H present near by C.

5. The phenyl ring is resonated at delta 7.4 as a multiplet due to monosubst. benzene.

For 13C-nmr spectrum:

For mono subst. benzene three different carbons (o-, m- and p-) resonated at about (127.7 ppm, 128 and 126.1 ppm).

And two different carbons are present in vinyl group which resonated at about 113 and 136 ppm.

And one subst. carbon of benzene ring is resonated at about 137 ppm.

Hence 6 different carbons resonated at different chemical shifts.