Acetaldeunge Lab Report

Acetaldeunge Lab Report

For example the wave numbers of v (C=O) absorptions for the following compounds:

Formaldehyde (HCHO) 1750 cm–1.

Acetaldehyde (CH3CHO) 1745 cm–1.

Acetone (CH3COCH3) 1715 cm–1.

Introduction of an electronegative group causes –I effect which results in the bond order to increase.

Hence the force constant increases and the wave number of absorption rises. MESOMERIC EFFECT It is responsible for lengthening or the weakening of a bond thus causing lowering of absorption frequency. Since nitrogen atom is less electronegative than oxygen atom, the electron pair on nitrogen atom in amide is more labile and hence it participates more in conjugation.

Due to this greater degree of conjugation, the C=O absorption frequency is much less in amides as compared to that in esters.

FIELD EFFECT In ortho substituted compounds, the lone pair of electrons on two atoms influences each other through space interactions and changes the vibrational frequencies of both the groups.

This effect is called field effect. Interpretation of spectra–

1. N–H stretching vibrations (secondary amine) Secondary amines show a single weak band in the 3350 – 3310 cm–1 region. These bands are shifted to longer wavelengths than primary amines due to hydrogen bonding. The position, intensity and the breadth of the band indicates whether the group is free, exhibit intermolecular hydrogen bonding.

2. C–H stretching vibrations (Aromatic/Aliphatic) Aromatic C–H stretching bands occur between 3100 and 3000 cm–1. Weak combination and overtone bands appear in the 2000–1650 cm–1 region. The absorption due to C–H stretch from methyl or methylene groups occur in the region of 3000–2840 cm–1

3. Ring stretching vibrations (C=C & C=N stretching vibrations) Ring stretching vibrations occur in the general region between 1600 and 1300 cm–1. The relative intensities and the band pattern depend on the substitution pattern and the nature of the substituent. 4 C–N stretching vibrations (secondary amines) – Aromatic amines display strong C–N stretching absorption in the 1342–1266 cm–1 region.

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