Question

) The spectra below are of acetone, 1,2-dichloroethane, 1,1,2-trichloroethane, 2,2-dimethoxypropane, I- bromopropane and 2-bromopropane. Assign them. b) c) d)

Answer 1

For (6) -

(a) is the spectra of 1,2 dichloroethane. It has two CH₂ groups which are chemically equivalent. So, they show only one peak. And due to higher electronegativity of chlorine , they appear at downfield.

(b) is the spectra of 2,2 dimethoxy propane. There are two chemically different types of protons and therefore show 2 peaks. The protons of methoxy group appear downfield.

(c) is the spectrum of 2-bromopropane. They are two chemically different types of protons. The proton attached to the carbon bearing bromine atom appears downfield and shows a septet due to 6 neighbouring protons, as it follows the n+1 rule where n= no. of neighbouring protons.

(d) is the spectrum of acetone. It shows a single peak as there are only one type of protons.

(e) is the spectrum of 1,1,2- trichloroethane. The carbon bearing two chlorine atoms reduces the electron density if the proton attached to the same proton, as a result of which this proton appears at downfield and the proton at other carbon has a peak at a lesser chemical shift than the former one.

( f) is the spectrum of 1- bromopropane. As it is the only compound which has 3 chemically different types of proton which shows 3 peaks.

For (7) -

1st graph is the spectrum of 1,2- dibromo-2-methyl propane. It is the only compound which has three chemically different types of protons and shows three peaks.

2nd graph is the spectrum of 1,4- dimethoxybenzene. There are 2 chemically different types of protons. As methyl group is attached to oxygen, it appears at downfield.

3rd graph is the spectrum of 1,4- dimethylbenzene. Here, there are two chemically different types of protons which shows two peaks.