16-38 (a) The fonnula CgH70CI has five elements of unsaturation, probably a benzene ring (4) plus either a double bond or a ring. The IR suggests a conjugated carbonyl at 1690 cm-1 and an aromatic ring at 1602 cm-I. The NMR shows a total of five aromatic protons, indicating a monosubstituted benzene. A 2H singlet at 8 4.7 is a deshielded methylene. < > o I I + C + CI } o o-� C- CH I 2 -CI (b) The mass spectral evidence of molecular ion peaks of 1 : 1 intensity at 1 84 and 1 86 shows the presence of a bromine atom. The rnlz 1 84 minus 79 for bromine gives a mass of 1 05 for the rest of the molecule, which is about a benzene ring plus two carbons and a few hydrogens. The NMR shows four aromatic hydrogens in a typical para pattern (two doublets), indicating a para-disubstituted benzene. The 2H quartet and 3H triplet are characteristic of an ethyl group. -0-+ Br + 16-39 (a) � like the ends of a � conjugated diene � � } Br-o-CH2CH3 o Diels·Alder product 16-40 new sigma bonds shown in bold
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