Question

Draw the arrow-pushing mechanism of a generic esterification reaction: b) From the spectral data (NMR, IR, MS) you were given, identify the structure of your ester product. c) Based on your answer to part b), what is the structure of your starting alcohol? 2) Critical analysis (6 points): a) Fully assign the 1H NMR spectrum of your product (i.e. determine which peaks in the 1H NMR correspond to which hydrogens in the product). You will not receive full marks for determination of the unknown unless you assign the 1H NMR spectrum completely. b) You will notice that we gave you the m/z value of the M+ ion of your product on the EI (electron impact) mass spectrum, but the actual peak on the spectrum is very small (or even non-existent). Read Solomons chapter 9 and explain why the M+ peak is so small.

Answer 1

See explaination for detailed answer

Step-by-step explanation:

In the IR spectrum, the broad peak at 3322 cm-1 corresponds to OH stretching while the peaks at 2929-2961 cm-1 correspond to C-H stretching. Thus the presence of alcohol is evident in the IR spectrum.

The 13C NMR suggests the presence of seven C-atoms in this ester. The peak corresponding to carbonyl carbon appear most downfield at ~172 ppm. The other six peaks are in the aliphatic region suggesting an aliphatic ester.

In the 1H NMR, we see a singlet at 2.0 ppm with the integral value of 3. This singlet is characteristic to the protons of the acetate (CH3CO) group as seen in ethyl acetate. This suggests that the acetic acid was employed in this esterification reaction. Using this information along with what we know from 13C NMR we can be certain that the given alcohol contains 5 carbons (total 7 carbon – 2 carbon from acetate group). Therefore the starting material must be pentyl alcohol.

The 1H NMR peaks for the pentyl group are

The most downfield triplet at 4.1 ppm corresponding to OCH2. This is due to deshielding of the CH2 by the electronegative O-atom

The most upfield triplet at 0.9 ppm corresponding to CH3.

A multiplet at 1.3 ppm corresponding to CH2 CH2 which is attached toCH3 moiety

A pentate at 1.6 ppm corresponding to CH2 which is attached toOCH3 moiety

Therefore, the given alcohol is n-pentyl alcohol and the ester is pentyl acetate (Molar mass 130.0994)

See attachment for diagram