Question

A compound, \(\mathrm{C_{15}H_{16}O_2}\), has the following spectral data; 
\(^1\)H NMR (ppm): 9.16 (s), 6.89 (d, \(J = 8\) Hz), 6.64 (d, \(J = 8\) Hz), 1.53 (s) 
\(^ {13}\)C NMR (ppm): 154.7, 140.9, 127.1, 114.4, 40.7, 30.7 
The structure of the compound is 

 

Hint:

Para-disubstituted benzene often shows two aromatic doublets (AA'BB') with \(J \approx 7\!-\!9\) Hz. A singlet near \(1.4\!-\!1.6\) ppm integrating to 6H commonly signals a gem-dimethyl \(\mathrm{C(Me)_2}\) attached to an sp\(^2\)/heteroatom center. Phenolic OH in non-deuterated solvents can appear broad/singlet near \(9\!-\!10\) ppm.

Answer 1

Step 1: Use formula and unsaturation. For \(\mathrm{C_{15}H_{16}O_2}\), the double-bond equivalents (DBE) are \[ \text{DBE}=\frac{2C+2-H}{2}=\frac{2(15)+2-16}{2}=8, \] consistent with two benzene rings (8 DBE). Thus two phenyl rings plus two oxygens are likely.
Step 2: Interpret \(^1\)H NMR.
\(\delta 9.16\) (s) \(⇒\) strongly deshielded phenolic \(\mathrm{OH}\) (often a singlet). One signal suggests two equivalent OH groups.
\(\delta 6.89\) (d, \(J=8\) Hz) and \(\delta 6.64\) (d, \(J=8\) Hz) \(⇒\) AA'BB' pattern of a para-disubstituted phenyl ring; equivalence on both rings implies a symmetric molecule. \(\delta 1.53\) (s) \(⇒\) six protons of two equivalent methyl groups on a quaternary carbon \(\big(\mathrm{C(Me)_2}\big)\).
Step 3: Interpret \(^ {13}\)C NMR.
154.7 ppm: phenolic \(\mathrm{C{-}O}\) ipso carbon.
140.9 ppm: quaternary aromatic carbon (para junction).
127.1, 114.4 ppm: substituted aromatic CH carbons of a para-disubstituted ring (two unique signals due to symmetry).
40.7 ppm: quaternary \(\mathrm{C(Me)_2}\) carbon.
30.7 ppm: methyl carbons of \(\mathrm{C(Me)_2}\).
Step 4: Match with options.
(B) and (C) would show OMe singlets near \(\sim 3.7\) ppm in \(^1\)H NMR, absent here \(⇒\) not possible. (D) has additional ring–\(\mathrm{CH_3}\) groups that would give \(\sim 2.3\) ppm benzylic methyl signals, not observed
(A) \(\mathrm{HO{-}Ph{-}C(Me)_2{-}Ph{-}OH}\) (bisphenol A core) fits all: symmetric para-disubstituted rings, two equivalent phenolic OH (\(\delta \sim 9\) ppm), and a \(\mathrm{C(Me)_2}\) singlet at \(\delta 1.5\) ppm, with matching \(^ {13}\)C shifts (30.7, 40.7 ppm).
Therefore, the structure is option (A).