Question

What are the typical IR and NMR spectral characteristics of cinnamaldehyde, acetone, dicinnamalacetone, and cinnamaldehyde?

Answer 1

IR, PMR, CMR spectral characteristics for Acetone, Cinnamadehude, Dicinnamalacetone are show below( Same colour used from chemically equivalent protons within the molecule. Same colour of protons or carbons in different structure doesn't mean thatthey are having equal chemical shifts)

1) Acetone:

A) IR spectra: 1720 cm^-1 for C=O, and <3000 cm^-1 for sp3 C-H stretch in -CH3.

B) PMR spectra : only one singlet peak at 2.1 ppm for 6H.

C) CMR spectra: 2 peaks, 210 ppm for Carbonyl C and 30 ppm for methyl C.

2) Cinnamadehyde:

A) IR spectra:

i) 2 peaks 2750 and 2850 cm-1 for aldehydic sp2 C-H stretch.

ii) Sharp 1680 cm-1 for strongly and extensively conjugated C=O.

iii) Sharp 1640 cm^-1 for ,- C=C and 1600 cm^-1 for aromatic C=C.and one extra oop at 1475 cm^-1

iv) many absorption >3000 cm^-1 for sp2 C-H stretch

B) PMR spectra: 4 Kinds of protons hence 4 peaks.

i) Aldehydic H at (9ppm, s)

ii) 2 olefinic proton peaks due to conjugation of C=C in C=O which makes C electrophilic and hence H downfield.

iii) 2 sets of aromatic protons.

C) CMR spectra : 7 kinds of C hence 7 peaks. shown in diagram.

3) Dicinnamylacetone:

A) IR spectra :Further lower C=O stretching peaks, no aldehydic stretches.

b) PMR spectra: 6 kinds of protons so 6 peaks. no aldehydic peak at 9 ppm.

c) CMR spectra: 9 kinds of C so 9 peaks in CMR.