OBSERVATIONS OF NONADDITIVE SUBSTITUENT EFFECTS ON THE DIMETHYL-SULFOXIDE SOLUTION HOMOLYTIC BOND STRENGTHS OF ANTHRYLMETHYL C-H BONDS

被引:12
作者
BAUSCH, MJ
GUADALUPEFASANO, C
PETERSON, BM
机构
[1] Department of Chemistry and Biochemistry, Southern Illinois University at Carbondale, Carbondale
关键词
D O I
10.1021/ja00022a027
中图分类号
O6 [化学];
学科分类号
0703 ;
摘要
Acid-base and redox data, when incorporated into a thermochemical cycle, enable accurate determination of the effects of substitutents on the homolytic strengths of chemical bonds. In this study, the effects of substitutents on the dimethyl sulfoxide phase homolytic strengths of labile sp3 C-H bonds present in 9-methylanthracene, seven variously substituted 9-methylanthracenes, phenylacetonitrile, and alpha-methoxyphenylacetonitrile are evaluated. The bond-strength data for these species indicate that, when present individually, 10-cyano and alpha-methoxy substitutents weaken the anthrylmethyl C-H bond in 9-methylanthracene (in a homolytic sense) by 1-2 and 4 kcal/mol, respectively. When both 10-cyano and alpha-methoxy substituents are present in the same molecule, as in 10-cyano-9-(methoxymethyl)anthracene, the anthrylmethyl sp3 C-H bond is weakened by 8 kcal/mol. Therefore, the bond-weakening effect of a 10-cyano substituent on 9-methylanthracene sp3 C-H bond strengths is ca. 2kcal/mol greater when the C-H bond to be cleaved is adjacent to an alpha-methoxy substituent. A similar and somewhat larger synergism (ca. 4 kcal/mol) is observed when an alpha-phenoxy substituent is present in place of alpha-methoxy. In related experiments, an alpha-cyano substituent is shown to weaken the anthrylmethyl C-H bond in 9-methylanthracene by ca. 3 kcal/mol. These data constitute the first nonkinetic experimental observations of synergistic substituent effects on the homolytic strengths of sp3 C-H bonds. While not necessarily indicative of a general phenomenon, the observed changes in 9-methylanthracene sp3 C-H homolytic bond strengths (due to the simultaneous presence of alpha-methoxy (or alpha-phenoxy) and 10-cyano substituents) can be rationalized by invoking a solvent-induced stabilization in the incipient anthrylmethyl radicals that results from the presence of both donor and acceptor substituents in conjugation with the unpaired electron.
引用
收藏
页码:8384 / 8388
页数:5
相关论文
共 40 条
  • [21] THE 2 HYDROGEN-OXYGEN BOND-DISSOCIATION ENERGIES OF HYDROQUINONE
    FRIEDRICH, LE
    [J]. JOURNAL OF ORGANIC CHEMISTRY, 1983, 48 (21) : 3851 - 3852
  • [22] REEVALUATION OF THE BOND-DISSOCIATION ENERGIES (DELTA-HDBE) FOR H-OH, H-OOH, H-OO-, H-O., H-OO-, AND H-OO.
    GOLDEN, DM
    BIERBAUM, VM
    HOWARD, CJ
    [J]. JOURNAL OF PHYSICAL CHEMISTRY, 1990, 94 (13) : 5413 - 5415
  • [23] GREEF R, 1985, INSTRUMENTAL METHODS, P195
  • [24] ELECTROCHEMISTRY IN MEDIA OF INTERMEDIATE ACIDITY .7. REDOX EQUILIBRIA OF ANTHRACENE CATION RADICALS, DICATIONS, AND CATIONIC ADDITION-PRODUCTS
    HAMMERICH, O
    PARKER, VD
    [J]. JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 1974, 96 (13) : 4289 - 4296
  • [25] JIRKA GPM, 1990, THESIS SO ILLINOIS U
  • [26] A QUANTITATIVE ASSESSMENT OF THE MEROSTABILIZATION ENERGY OF CARBON-CENTERED RADICALS
    KATRITZKY, AR
    ZERNER, MC
    KARELSON, MM
    [J]. JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 1986, 108 (23) : 7213 - 7214
  • [27] KITRITZKY AR, 1974, J CHEM SOC P1, P1427
  • [28] ABSOLUTE RATES FOR DIMERIZATION OF CAPTO-DATIVE SUBSTITUTED METHYL RADICALS IN SOLUTION - ABSENCE OF KINETIC STABILIZATION
    KORTH, HG
    SUSTMANN, R
    MERENYI, R
    VIEHE, HG
    [J]. JOURNAL OF THE CHEMICAL SOCIETY-PERKIN TRANSACTIONS 2, 1983, (01): : 67 - 74
  • [29] LOUW R, 1983, J R NETH CHEM SOC, V110, P119
  • [30] EQUILIBRIUM ACIDITIES OF CARBON ACIDS .6. ESTABLISHMENT OF AN ABSOLUTE SCALE OF ACIDITIES IN DIMETHYL-SULFOXIDE SOLUTION
    MATTHEWS, WS
    BARES, JE
    BARTMESS, JE
    BORDWELL, FG
    CORNFORTH, FJ
    DRUCKER, GE
    MARGOLIN, Z
    MCCALLUM, RJ
    MCCOLLUM, GJ
    VANIER, NR
    [J]. JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 1975, 97 (24) : 7006 - 7014