Chapter 20, Problem 20.71P

Interpretation Introduction

Interpretation:

The product for the given reaction is to be determined, and the complete, detailed mechanism for the same reaction is to be drawn from the given data.

Concept introduction:

In ^{${}^1\text{H}$} NMR spectroscopy, protons in different environments within a molecule have different chemical shifts; that is, they experience different degrees of shielding.

In addition to chemical shift, a ${}^1\text{H}$ NMR spectrum provides structural information based on: Number of signals, which tells how many different kinds of protons are there; Integrated areas, which tells the ratios of the various kinds of protons; and, Splitting pattern, which gives information about the number of protons that are within two or three bonds of the one giving the signal. Spin–spin splitting of NMR signals results from the coupling of the nuclear spins that are separated by two bonds (geminal coupling) or three bonds (vicinal coupling). In these cases, the number of peaks into which a signal is split is equal to $\text{(n+1)}$, where n is the number of protons to which the proton in question is coupled. Protons that have the same chemical shift do not split each other’s signals.

Complicated splitting patterns can result when a proton is unequally coupled to two or more protons that are different from one another.

The ideal range for alkane protons is $\text{δ}0.9\text{- δ}1.4$; for alcohol it is $\text{δ}2\text{- δ}5.0$; and, for aromatic protons it is $\text{δ}6.5\text{- δ}8.5$. The chemical shift of a signal prompts about the aromatic rings, double bonds, or nearby electronegative atoms. Generally, protons of methylene group attached to O atom (in ether or ester) occurs at above $\text{δ}3.0$, and values depend on other environments also. The integration of each signal suggests the number of protons responsible for that signal. The splitting pattern of a signal indicates the number of neighboring protons that are distinct from the protons responsible for that signal. Based on the data given in the ${}^1\text{H}$ NMR build molecular fragments with multiple carbon atoms. Lithium aluminum hydride is a strong reducing agent and reduces almost all types of acid derivatives. For example, an ester is reduced to corresponding primary alcohol through successive nucleophilic addition-elimination mechanism and acid or protic workup step is required to get uncharged alcohol.