1559Tch20358-37210/18/055:03Page370 EQA 370.chapter 20 CARBOXYUC ACID DERIVATIVES 9Sah .(a)Collect your ind decide what it tls you.Beginh and contains only C.H.andO. match the remnwith the msof som combntioofoand hydrogens: 风 840939 Now turn to the proton NMR.You have the following absorptions: =1.1:Triplet,integration of 3 H:a CHCHa-group =1.2:Doublet,integration of 6 H:a(CH)CH-group OCH(CH3) of a lar ne es s you c60. 61. (a) Collect your information and decide what it tells you. Begin with the molecular ion. It is a single peak, ruling out Cl or Br, which would give two peaks two mass units apart. The value is an even number, therefore one N atom cannot be present (see Exercise 11-13 on text page 468; zero or an even number of nitrogen atoms is required for an even mass number). The IR absorption is closest to the ester range, so you should operate under the initial assumption that the molecule is an ester and contains only C, H, and O. The exact mass will give you the molecular formula, with a bit of work. The ester function contains two oxygens, so subtract their mass (2
15.9949) from that of the parent ion and try to match the remainder with the mass of some combination of carbons and hydrogens: The only reasonable combination of C and H that has a mass of 84 is C6H12. Does it match exactly? (6
12) (12
1.00783) 84.0940—yes, indeed it does. (If that had not been the case, you would have had to explore possibilities containing oxygen, such as C5H8O, etc.) The molecular formula is C6H12O2, giving one degree of unsaturation, the ester carbonyl group. Now turn to the proton NMR. You have the following absorptions:  1.1: Triplet, integration of 3 H; a CH3OCH2O group  1.2: Doublet, integration of 6 H; a (CH3)2CHO group  2.3: Quartet, integration of 2 H; indicates a CH3OCH2O group, possibly attached to a carbonyl carbon due to the slightly deshielded position in the spectrum  5.0: A septet (see amplified scan), integration of 1 H; seven lines imply two methyl groups as neighbors; chemical shift indicates attachment to oxygen: a (CH3)2CHOOO group O B Do you have your answer? Yes: CH3CH2COOCH(CH3)2 Does this fit the rest of the data? The upfield region of the NMR spectrum can now be interpreted as consisting of a large doublet for the methyls of the CH(CH3)2 group, overlapping one peak of a smaller triplet, which arises from the CH3 of the ethyl group. How about the mass spectrum? The base peak at m/z 57 arises from a type of  cleavage at the ester COO bond, giving the very stable acylium ion CH3CH2CqO. See how many of the other fragments you can assign. 116.0837 (2
15.9949)  84.0939 H2NNH2, KOH,  (Wolff-Kishner) C O O H O H H, H2O (conc.) CH3 O O product H CN O H H, HOCH2CH2OH (Protect ketone) 2. H, H2O (dilute) 1. [(CH3)2CHCH2]2AlH (Don’t want to deprotect ketone until after next step!) CN O O H 370 • Chapter 20 CARBOXYLIC ACID DERIVATIVES 1559T_ch20_358-372 10/18/05 5:03 Page 370