Organic chemistry help please?

Question

Explain how you could distinguish between a sample of 1bromopropane and 2 bromopropane using:
a) infra-red spectroscopy
b)low-resolution proton n.m.r spectroscopy

they are different samples

Answer 1

1-bromopropane = BrH2C-CH2-CH3
2-bromopropane = H3C-CHBr-CH3

This would be challenging to distinguish with IR, since the C-Br band is around 640 cm^-1. But the C-CH3 band in 2-bromopropane would be stronger, since you have twice as many methyl groups with the secondary halide than the primary halide.

However, the difference would be readily apparent by NMR -- 2-bromo would have only two types of protons -- methyl (6) and a single proton in the -CHBr-, whereas the 1-bromo will have three methyl protons, two methylene protons (-CH2-), and two bromomethyl protons (H2BrC-).

Check your friendly local CRC handbook for some approximate spectral correlations . . .

Hope this helps.

Answer 2

with infrared it would be difficult since it is used mainly for functional group which these two are the same.

with NMR
the 2-bromopropane would have 2 groups: 1 group being a triplet 6H tall, and the 2 being a septet 2H tall.
the 1-bromopropane would have 3 groups: 1 group being a triplet 2H tall, the 2 being a hextet 2H tall, and the 3 group being a triplet 3H tall.

the big difference being the number of cluster's.

Answer 3

eh they are both the same samples

Answer 4

they are different in structure formula
Br ] Br
I I I ] I I I
- c-c-c- ] - c-c-c-
I I I ] I I I