Organic Chemistry Tue Oct 31 12 06 01 2017 (GMT-05:00) 70 60 50 : 40 20 10 -10 4

Question

Organic Chemistry
Tue Oct 31 12 06 01 2017 (GMT-05:00) 70 60 50 : 40 20 10 -10 4000 3500 3000 2500 2000 1500 1000 Wavenumbers (cm-1) Tue Oct 31 12:07:44 2017 (GMT-05:00) FIND PEAKS: Tue Oct 31 1206:01 2017 (GMT-05:00) 000.00 400.00 Spectrum Region: Absolute threshold: 59.087 Sensitivity: Peak list 50 Position: 568.16 tensity: 57.957 Position:654.78 Intensity. 55.641 Position: 69081 ntensity 8.444 Position: 728.47 Intensity 36.567 Position: 737.08 Intensity: 35.582 Position: 752.27 Intensity: 22.684 Position: 967.06 Intensity: 46740

Explanation / Answer

The strong C=O stretching frequency occurs around 1686 cm-1; this is characteristic of an aryl ketone or an aromatic compound containing a keto group and hence we can rule out cyclohexanone, methyl isobutyl ketone, 3-methylcylohexanone, propionaldehyde and pinacolon. We will not rule of ethyl acetate since, the C-O linkage in ethyl acetate causes a shift of the C=O stretching frequency to lower wavenumbers.

Aldehydes show two peaks due to the O=C-H group at around 2750 cm-1 and 2850 cm-1. The given spectrum lacks peaks in the said region and consequently, the compound cannot be an aldehyde. Consequently, rule out benzaldehyde, anisaldehyde and hexanal (all are aldehydes).

C-O group in esters show strong absorption around 1000-1300 cm-1. The absorption shows up as two or more bands of strong intensity. The said region of the spectrum contains a few bands and hence, we are likely to assume the compound is the ethyl acetate. However, ethyl acetate is a simple ester and conjugation effects cannot lower the C=O stretching frequency to such low values (normal C=O stretching frequency in esters is 1730-1750 cm-1). Consequently, we rule out ethyl acetate.

The spectrum is most likely due to valerophenone. Conjugation with the phenyl group lowers the C=O frequency to 1686 cm-1. The peaks around 2800-3000 cm-1 are due to C-H stretching of the alkyl groups. C=C stretching of the aromatic ring occurs as multiple weak bands around 1400-1600 cm-1 (ans).

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