Chapter 16, Problem 45PP

Interpretation Introduction

Interpretation: For the given compounds the chemical shift values of the signals to be predicted.

Concept Introduction:

Chemical shift: The frequency of the proton signal in the spectrum with reference to the standard compound  which may be TMS(Tetramethylsilane) shows signal at 0 ppm(parts per million).

$\text{Chemical}\text{shift}\text{=}\frac{\text{signal}\text{frequency-}\text{reference}\text{frequency}}{\text{frequency}\text{of}\text{spectrometer}}\left({\text{10}}^{\text{6}}\right)$

Bench mark values: The chemical shift values to remember for the protons below.

Methyl	$\text{0}\text{.9}$ (chemical shift)
Methylene	$\text{1}\text{.2}$ (chemical shift)
Methine	$\text{1}\text{.7}$ (chemical shift)

Inductive effect: The presence of functional groups at the alpha position has impact on the protons

FUNCTIONAL GROUP	EFFECT ON THE ALPHA PROTONS	EFFECT ON THE BETA PROTONS
Oxygen of an alcohol or ether	$\text{+2}\text{.5}$	$\text{+0}\text{.5}$
Oxygen of ester	$\text{+3}\text{.0}$	$\text{+0}\text{.6}$
Carbonyl groups	$\text{+1}\text{.0}$	$\text{+0}\text{.2}$

Chemical shift values for protons in different electronic environment:

Types of protons	Chemical shift
Allylic	$\text{~2}$
Alkynyl	$\text{~2}\text{.5}$
Aromatic methyl	$\text{~2}\text{.5}$
Alkyl halide	$\text{~2-4}$
Alcohol	$~2-5$
Vinyl	$~4.5-6.5$
Aryl	$~6.5-8$
Aldehyde	$~10$
carboxylic	$~12$