Chapter 16, Problem 54P

Interpretation Introduction

Interpretation:

The structure of the product on the basis of mass spectra, IR and NMR data is to be determined.

Concept introduction:

Hydrogenolysis reaction of benzyl alcohols results in the cleavage of the benzyl and oxygen bond. It may also involve group migration, which is usually carried out by the phenyl ring.

Infrared absorption bands indicate the functional groups present in a compound. For example, carbonyl group shows a band from $1600\text{ to }1750{\text{ cm}}^{\text{-1}}$, hydroxyl group shows a band from $\text{3400 to 35}50{\text{ cm}}^{\text{-1}}$. So, if a compound shows a band in the carbonyl range only, it is an aldehyde or ketone, while if it shows one in the region of hydroxyl, it is an alcohol or a phenol. If two bands are observed with one in each region, it is a carboxylic acid.

NMR data indicates the number and types of protons or carbons present in a compound based on the number of signals obtained in ${}^1\text{H}$ NMR or ${}^{13}\text{C}$ NMR, respectively. ${}^1\text{H}$ NMR signals are often with multiplicity such as doublets and triplets, which indicates the number of protons present on the carbons adjacent to that proton. The protons of an aromatic ring show a signal from $6.5–7.5\text{ ppm}$, those of alkyl group from $0.5\text{ to }1.5\text{ ppm}$ while alkyl groups adjacent to a carbonyl group or oxygen atom show signals from $2.0\text{ to }3.0\text{ ppm}$. Alcohol group shows a signal from $2.0\text{ to }3.0\text{ ppm}$ but is always a singlet.

The mass spectra of a compound indicate the molecular ion peak, which give the molecular mass of the compound.