meta versus para substitution: how does C-H activation in a methyl group occur in 3-methylbenzophenone but does not take place in 4-methylbenzophenone?
Title | meta versus para substitution: how does C-H activation in a methyl group occur in 3-methylbenzophenone but does not take place in 4-methylbenzophenone? |
Publication Type | Journal Article |
Year of Publication | 2013 |
Authors | Ma, Jiani, Su Tao, Li Ming-De, Zhang Xiting, Huang Jinqing, and Phillips David Lee |
Journal | The Journal of organic chemistry |
Volume | 78 |
Issue | 10 |
Pagination | 4867-78 |
Date Published | 2013 May 17 |
ISSN | 1520-6904 |
Abstract | The photophysical and photochemical reactions of 3-methylbenzophenone (3-MeBP) and 4-methylbenzophenone (4-MeBP) were investigated using femtosecond transient absorption (fs-TA) and nanosecond time-resolved resonance Raman (ns-TR(3)) spectroscopy and density functional theory (DFT) calculations. 3-MeBP and 4-MeBP were observed to behave similarly to their parent compound benzophenone (BP) in acetonitrile and isopropyl alcohol solvents. However, in acidic aqueous solutions, an unusual acid-catalyzed proton exchange reaction (denoted the m-methyl activation) of 3-MeBP (with a maximum efficiency at pH 0) is detected to compete with a photohydration reaction. In contrast, only the photohydration reaction was observed for 4-MeBP under the acidic pH conditions investigated. How the m-methyl activation takes place after photolysis of 3-MeBP in acid aqueous solutions is briefly discussed and compared to related photochemistry of other meta-substituted aromatic carbonyl compounds. |
DOI | 10.1021/jo400413t |
Alternate Journal | J. Org. Chem. |