Question

1.Which C = O aliphatic group absorbs more to the right of the IR spectrum? Show an example and explain the reason.

2. What functional groups show characteristic absorptions in the region of traces of the IR spectrum? Provide one molecule for each case

3.What is the expression for the Planck equation as a function of the wave number? Apply it to calculate the energy when  is equal to 3.0 μ. Emphasize the units

Answer 1

1) Amide is having the least value for stretching frequency for C=O stretching,

amide= 1630-1690 cm-1

carboxylic acid : 1705-1720 cm-1

acid anhydride: 1730 cm-1

esters: 1730-1740 cm-1

ketone: 1715 cm-1

aldehyde: 1720-1740 cm-1

acyl chloride: 1780-1820 cm-1

an IR spectrum has x-axis moving from higher values of stretching frequencies to lower frequencies towards the right. thus the least stretching frequency bond will appear on the right part of the spectrum . an amide is having the least stretching frequency.

Due to the easy donation of lone pairs and low electronegativity of N atom, resonance f lone pair of electrons is frequent from N to C=O bond, more frequent the electron shift towards the more electronegative O atom, more the single bond character in C=O. thus more the single bond character, lesser will be the force constant of that bond. thus lesser will be its stretching frequency. more the electronegativity difference between the two atoms, more will be the stretching frequency between the bond formed between them