The effect of the methoxy group on the geometry of the benzene ring supported by crystal structure studies and Ab Initio Calculations. Crystal and Molecular Structure of 4-(4-Methoxyphenyl)-2,6-diphenylpyridine and 1-Methyl-4-(4-methoxy-phenyl)-2,6-diphenylpyridinium perchlorate.

Krygowski, T.M.; Anulewicz, R.; Jarmuła, Adam; Ba̧k, Tomazz; Rasała, Danuta; Howard, S. T.

doi:10.1016/s0040-4020(01)89325-x

Cited by 27 publications

(17 citation statements)

References 13 publications

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“…It was observed (ab initio optimisation at HF/6-31G* level of theory) 27 that the methoxy-group in anisole causes nonequal bond lengths C 1 -C 2 and C 1 -C 6 in the ring (see Figure 3). The C 1 -C 2 bond 'under' the MeO group becomes slightly shorter than the C 1 -C 6 bond.…”

Section: Phenomenological Picture Of the Angular Group Induced Bond Amentioning

confidence: 99%

Angular Group Induced BondAlternation (AGIBA). A New Face of Substituent Effect Detectedin Molecular Geometry

Krygowski¹,

Cyrański²

2003

Synlett

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Angular Group Induced Bond Alternation is a new face of a substituent effect well documented by careful analysis of molecular geometry. The angular groups attached to monocyclic 6-πelectron systems cause substantial changes to π-electron distribution in the ring. Different patterns are found for X-Y and X=Y types of groups. The overall effect is due to the rehybridization effect, the through space π-electron interactions between a group and the ring, possibly also by other subtle effects, eg. the negative hyperconjugation. The effect is strongly conformational dependent. While the AGIBA is energetically weak, it is structurally strong enough that other interactions in monocyclic systems, eg. through -resonance type interactions do not reduce it. In polycyclic benzenoid hydrocarbons AGIBA works only locally while in non-cyclic π-electron systems the effect does not work at all.

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Section: Phenomenological Picture Of the Angular Group Induced Bond Amentioning

confidence: 99%

Angular Group Induced BondAlternation (AGIBA). A New Face of Substituent Effect Detectedin Molecular Geometry

Krygowski¹,

Cyrański²

2003

Synlett

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“…In contrast to the structural patterns of pyryliums noted above, structural studies on monocyclic N-benzylpyridiniums 14 suggest unavoidable steric compressions between the Nbenzyl group and substituents and pendant 2-and 6phenyls. The crystal structures of 2,4,6-triphenyl-Nmethylpyridinium tetrafluoroborate 2 and of 1-methyl-4-(4-methoxyphenyl)-2,6-diphenylpyridinium perchlorate 15 showed the heterocyclic ring to adopt a flattened boat conformation, and that while the dihedral angle between the heterocyclic ring and pendant phenyl on the 4-position were small (ca 25°), those at the 2-and 6positions were much larger (ca 55°), reducing nonbonded interaction between o-hydrogens on these phenyls and the N-methyl at the expense of reduced overlap between the p-arrays of the pendant phenyls and the heteroaromatic central ring. We argue that these differences are reflected in r 1 because the radical places little demand on the substituents.…”

Section: Preparation Structure and Electro-chemistry Of Cationsmentioning

confidence: 99%

Substituent effects in reductions of heteroaromatic cations

Heyes

Menon

Watt

et al. 2002

J of Physical Organic Chem

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A set of 11 each of 2,4,6-triphenylpyrylium, -thiopyrylium and -N-methylpyridinium tetrafluoroborates carrying a range of substituents in the phenyl rings were prepared. First and second wave reduction potentials were determined. For the thiopyrylium series there are linear correlations between scaled potentials (E°/0.05915) and summed Hammett constants for substituents in the pendant phenyl groups ( = 2.29 and 3.38 for first and second waves respectively). For the pyrylium series, a good linear relationship ( = 2.79) is obtained for all substituent patterns for the first wave reduction potentials, but for the second wave there are separate correlations for salts carrying substituents in the 4-phenyl and for those carrying substituents in 2-and 6-phenyls. For the pyridinium series, the first wave potentials show separate correlations for salts carrying substituents in the 4-phenyl and for those carrying substituents in 2-and 6-phenyls, but a single linear relationship for the second wave potentials. These are related to particular structural features in the cations, radicals and anions in each series. Rates and products were determined for reductions of the pyrylium and thiopyrylium cations by sodium cyanoborohydride and of all cations by sodium borohydride in acetonitrile solution. Reactions are first order in reducing agent and cation. Primary kinetic isotope effects were determined for borohydride reduction of the least reactive of each of the series of cations. Plots of logarithms of second-order rate constants against summed Hammett constants for substituents in the pendant phenyl groups are linear for all combinations of reagent and cation with 0.91 < < 1.50 across all substituent patterns. For parent pyrylium and thiopyryliums, kBH 4 /kCNBH 3 = 8.4 Â 10 4 and 1.5 Â 10 4 , respectively, and for reductions by borohydride the reactivities of the pyrylium, thiopyrylium and pyridinium, series decrease in the order 1.4 Â 10 5 :8.8 Â 10 3 :1. Constant selectivities are not observed. Comparison of the correlations for electrochemical reduction and for hydride addition leads to the conclusion that charge neutralization in the hydride addition transition states runs ahead of bonding changes at the originating B-H bond.

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“…The effect of alternation of the ring bond lengths is best characterized by the HOSE model, 6 which permits the estimation of relative Kekulé structure contributions. In our previous study on anisole, 7 it was shown that the methoxy group induces shortening of the adjacent ring C-C bond cis to the OMe group. A remarkable finding was that, although the estimated through-space interaction energy between the methoxy group and the ring was small (ca 5 kJ mol…”

Section: Introductionmentioning

confidence: 95%

“…Hence there is qualitative similarity of the results with those for anisole. 7 Further theoretical investigations into the nature of this bond length fixation are under way. EXPERIMENTAL The x-ray structure determination at 100 K utilized equipment and techniques which have been described previously.…”

Section: Introductionmentioning

confidence: 99%

“…Moreover, it is in excellent agreement with the bond length alternation found in the ab initio calculation (0·018 Å). Figure 2 shows the two possible resonance structures, together with their relative contributions, computed using the HOSE model which requires only the bond lengths 7 (ab initio values in parentheses). An alternative measure of the -electron delocalization (i.e.…”

Section: Introductionmentioning

confidence: 99%

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