Question

Propose structures for the following isomeric alcohols that give the 13C NMR spectra below. Assign the carbons to their respective peaks. A table of chemical shifts is located on page 43.

09 13C shift chart 304.pdf

Answer 1

Answer 2

A) The C -13 has five peaks corresponding to all five carbons of C5H12O.

The DEPT135 shows four negative peaks corresponding to 4 CH2 ggroups, one very much down field at 62.8 which is attached to the -OH group. It shows one positive peak which corresponds to methyl at 14.0ppm

The DEPT 90 shows no peak whcih shows the absence of CH groups. {DEPT 90 shows only CH peaks)

The three peaks at 22.6, 28 , and 35 clearly show they are the CH2 in middle of the n-pentyl alcohol.

Thus the structure of A (C5H12O) is CH3CH2CH2CH2CH2OH

B) this is a secondary alcohol CH3CH(OH)CH2CH2CH3,2-pentanol

All five peaks are shown and two CH2 negative peaks in DEPT 135. and one CH in DEPT 90.much downfield due to the OH

C) This is also a secondary alcohol CH3CH2CH(OH)CH2CH3. 3-pentanol

The spectrum shows only 3 peaks as the two methyls are identical and two methylenes are identical.

DEPT 135 show three peaks , two methyls as one peak, both CH2 as single negative peak and one CH peak.

The presence of Ch confirmed by peak at 74.5 in DEPT 90.downfield due to the OH.