Strain Energies in Hydrocarbons from Heats of Combustion. III. 3,4,5,6- and 2,4,5,7-Tetramethylphenanthrenes<sup>1a</sup>

Karnes, Harold A.; Kybett, Brian D.; Wilson, Mary H.; Margrave, John L.; Newman, Melvin S.

doi:10.1021/ja00952a006

Cited by 33 publications

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“…These results support the idea of "buttressing" of substituents [9]. Additionally, extrapolate to ~5 = -342 when there are none, and so they are compatible with the t5 = -344.5 + 2.1 kJ mol -n for the parent benzoic acid case.…”

supporting

confidence: 81%

What are the relative steric demands of carboxyl and methyl groups?

et al. 1994

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The relative steric demands of carboxyl and methyl groups are compared by contrasting the difference quantity 5 -~ AH~'(g, ArCOOH) -AH~'(g, ARCH3) for a collection of alkylated benzoic acids and toluenes with the value for Ar = C6H5, the archetypical (i.e., unsubstituted) benzoic acid and toluene. We conclude that carboxyl and methyl groups are nearly the same size.KEY WORDS: Benzoic acids; enthalpy of formation; isomers; toluenes.This brief note discusses the relative steric demands of two of the most important groups in organic chemistry, --COOH and --CH 3. It seems almost obvious that --COOH is larger than --CH 3. After all, atomic oxygen is "bigger" than atomic hydrogen, and so a molecular group composed of a carbon with two oxygens and a hydrogen should be larger than a group composed of a carbon with three hydrogens. However, "size" is not the same as "steric demand." After all, the "lollipop stick" polyyne substituentshave increasing molar volume with increasing n, yet for all n > 0 they would be expected to "keep out of the way" of other groups to nearly identical amounts, and very probably, better than the t-butyl group that corresponds to the n = 0 case.How can we ascertain the steric demands of the COOH and CH 3 groups of interest? One way is to determine the steric demand of the two groups separately ~Instituto de Qufmica Ffsica "'Rocasolano," C.S.I.C., 141and take the difference of these quantities. It is important to specify the "environment" of these groups and to ensure that it is the same for both. We will take the environment to be aromatic rings for which there is an sp 2 carbon affixed to the COOH or the CH3. This suggests substituted benzoic acids, and in particular, one may define the steric demand of the COOH group by the difference of the (implicitly gas phase) enthalpies of formation of its o-and p-alkylated derivatives [1]. For R = CH3, C2H5, i-C3H 7, and t-C4H 9, the p-substituted benzoic acids (RC6H4COOH) are more stable than their o-isomers by 9.8 + 2.1, 15.4 + 2.6, 23.5 +__ 2.8, and 21.4 + 2.9 kJ mol -I, respectively. The corresponding p-alkyltoluenes (RC6H4CH3) are found to be more stable than their o-isomers by 1.1 + 1.5 (this, and all otherwise unreferenced enthalpy of formation data, is taken from Ref. ) kJ mol -I, respectively. In all cases, the p-disubstituted benzene is more stable than its o-isomer and in the cases of methyl, ethyl, and isopropyl substitution, the COOH group is considerably destabilized relative to CH 3. We would thus immediately conclude

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What are the relative steric demands of carboxyl and methyl groups?

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“…(2)]. [17] Treatment of 11 with SmI 2 gave the diequatorial isomer 12 a as the only trans-diol, consistent with the above mentioned data. [18] The synthetic scope of the present process is not restricted to natural product synthesis, [1] but has relevance to asymmetric synthesis: Application of the reaction to the enantiopure dialdehyde 14, readily obtained from the 2,2'-(S)-(À)-binaphthol-derived diester 13 [19] 2.…”

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confidence: 69%

From Axial Chirality to Central Chiralities: Pinacol Cyclization of 2,2′-Biaryldicarbaldehyde to trans-9,10-Dihydrophenanthrene-9,10-diol

Ohmori

Kitamura

Suzuki

1999

Angew. Chem. Int. Ed.

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Two salient features-the stereoselectivity to give only the trans-diol, and the stereospecificity to transmit the axial chirality (in case the starting biphenyl is configurationally stable) onto two stereogenic centers of the product-characterize the pinacol cyclization of 2,2'-biaryldicarbaldehydes (see reaction). The accessibility of trans-9,10-dihydrophenanthrene-9,10-diols provides the new enantiopure C -symmetric diol 1, which shows potential utility in asymmetric synthesis.

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“…Evaporation of a solution of these in ethanol/acetone produced satisfactory crystals. A synthesis is described by Karnes et al (1965).…”

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confidence: 99%

2,4,5,7-Tetramethylphenanthrene at 150 K

Gerkin¹

2000

Acta Crystallogr C

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The title compound, C(18)H(18), crystallized in the centrosymmetric space group P2(1)/c with one molecule as the asymmetric unit. The methyl-group H atoms at the 4 and 5 positions are ordered, while those at the 2 and 7 positions are disordered. The torsion of the bay region of the core is notably similar to that of other 4, 5-dimethylphenanthrenes. No substantial C-H.pi interaction occurs in this structure.

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Strain Energies in Hydrocarbons from Heats of Combustion. III. 3,4,5,6- and 2,4,5,7-Tetramethylphenanthrenes^1a

Cited by 33 publications

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What are the relative steric demands of carboxyl and methyl groups?

What are the relative steric demands of carboxyl and methyl groups?

From Axial Chirality to Central Chiralities: Pinacol Cyclization of 2,2′-Biaryldicarbaldehyde to trans-9,10-Dihydrophenanthrene-9,10-diol

2,4,5,7-Tetramethylphenanthrene at 150 K

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Strain Energies in Hydrocarbons from Heats of Combustion. III. 3,4,5,6- and 2,4,5,7-Tetramethylphenanthrenes1a

Cited by 33 publications

References 0 publications

What are the relative steric demands of carboxyl and methyl groups?

What are the relative steric demands of carboxyl and methyl groups?

From Axial Chirality to Central Chiralities: Pinacol Cyclization of 2,2′-Biaryldicarbaldehyde to trans-9,10-Dihydrophenanthrene-9,10-diol

2,4,5,7-Tetramethylphenanthrene at 150 K

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Strain Energies in Hydrocarbons from Heats of Combustion. III. 3,4,5,6- and 2,4,5,7-Tetramethylphenanthrenes^1a