Does 2-methylacetophenone comply with steric inhibition of resonance? A direct experimental proof of its nonplanar conformation from a joint ab initio/electron diffraction analysis

D. Hnyk; S. Samdal; O. Exner; D.A. Wann; D.W.H. Rankin

doi:10.1021/jo100291r

Does 2-methylacetophenone comply with steric inhibition of resonance? A direct experimental proof of its nonplanar conformation from a joint ab initio/electron diffraction analysis

D. Hnyk, S. Samdal, O. Exner, D.A. Wann, D.W.H. Rankin

Chemistry

Research output: Contribution to journal › Article › peer-review

Abstract

(Figure presented) The structure and conformations of 2-methylacetophenone (1) have been investigated by ab initio calculations carried out at the MP2(full)/6-311++G* level and by gas electron diffraction (GED). According to both methods, 1 exists predominantly as a form with the CεO bond synclinal with respect to the Car-C(O) bond (1B), with a torsional angle [C(6)-C(1)-CεO] of 32.7(24)° as determined by GED and 26.0° from MP2(full)/6-311++G. Calculations also predict the presence of a second conformer, the anticlinal structure (1C), with φ = 140.0°, with an abundance of less than 6%, an amount hardly detectable by GED. Different DFT computational protocols both support a nonplanar form of the predominant conformer (B2PLYP) and are in contradiction (B3LYP, M052x, B98, B97-D) with this experimental finding. The GED results, supported by the calculations that involve long-range correlation, are in a good agreement with 13C NMR spectroscopic investigations, UV spectra, and dipole moment studies. However, previous claims that assumed steric inhibition of resonance caused by a significantly nonplanar conformation with φ close to 90° have been disproved. Steric crowding is evident from the geometrical parameters, particularly from the C(1)-C(2) bond length and from the C(1)-C(2)-C(H 3) and C(2)-C(1)-C(O) bond angles. It is concluded that any explanation of reactivity by steric inhibition of resonance and by other steric factors must be supported by experimental and/or theoretical investigation of the actual molecular shape. © 2010 American Chemical Society.

Original language	English
Pages (from-to)	4939-4943
Journal	Journal of Organic Chemistry
Volume	75
Issue number	15
DOIs	https://doi.org/10.1021/jo100291r
Publication status	Published - 6 Aug 2010

Bibliographical note

Cited By (since 1996):2

Export Date: 1 October 2013

Source: Scopus

CODEN: JOCEA

doi: 10.1021/jo100291r

Language of Original Document: English

Correspondence Address: Hnyk, D.; Institute of Inorganic Chemistry of the ASCR, v.v.i., No. 1001, CZ-250 68 Husinec-Řež, Czech Republic; email: [email protected]

Chemicals/CAS: carbon, 7440-44-0; oxygen, 7782-44-7

References: Dippy, J.F.J., Hughes, S.R.C., Laxton, J.W., (1954) J. Chem. Soc., p. 1470; Wilson, J.M., Gore, N.E., Sawbridge, J.E., Cardenas-Cruz, F., (1967) J. Chem. Soc. B, p. 852; Charton, M., (1971) Prog. Phys. Org. Chem., 8, p. 235; Zalewski, R.I., Patai, S., (1992) The Chemistry of Functional Groups. Supplement B: The Chemistry of Acid Derivatives, 2. , Wiley: New York; Kukol, A., Strehle, F., Thielking, G., Grützmacher, H.F., (1993) Org. Mass Spectrom., 28, p. 1107; Decouzon, M., Ertl, P., Exner, O., Gal, J.-F., Maria, P.-C., (1993) J. Am. Chem. Soc., 115, p. 12071; Decouzon, M., Exner, O., Gal, J.-F., Maria, P.-C., (1996) J. Chem. Soc., Perkin Trans. 2, p. 475; Decouzon, M., Gal, J.-F., Maria, P.-C., Böhm, S., Jiménez, P., Roux, M.V., Exner, O., (1997) New J. Chem., 21, p. 561; Braude, E.A., Sondheimer, F., Forbes, W.F., (1954) Nature, 173, p. 117; Yates, K., Scott, B.F., (1963) Can. J. Chem., 41, p. 2320; Dhami, K.S., Stothers, J.B., (1965) Can. J. Chem., 43, p. 479; Guilleme, J., Diez, E., Bermejo, F.J., (1985) Magn. Reson. Chem., 23, p. 442; Oakley, M.G., Boykin, D.W., (1986) J. Chem. Soc., Chem. Commun., p. 439; Baumstark, A.L., Balakrishnan, P., Dotrong, M., McCloskey, C.J., Oakley, M.G., Boykin, D.W., (1987) J. Am. Chem. Soc., 109, p. 1059; Zaitsev, B.A., (1974) Izv. Akad. Nauk SSSR, Ser. Khim., p. 780; Lumbroso, H., Liegeois, C., Goethals, G., Uzan, R., (1983) Z. Phys. Chem., 138, p. 167; Smeyers, Y.G., Sieiro, C., (1979) Theor. Chim. Acta, 28, p. 355; Böhm, S., Exner, O., (2000) Chem.- Eur. J., 6, p. 3391; Böhm, S., Exner, O., (2001) New J. Chem., 25, p. 250; Tinant, B., Declercq, J.-P., Van Meerssch, M., Exner, O., (1988) Collect. Czech. Chem. Commun., 53, p. 301; Hnyk, D., Borisenko, K.B., Samdal, S., Exner, O., (2000) Eur. J. Org. Chem., p. 2063; Montaudo, G., Caccamese, S., Librando, V., Maravigna, P., (1975) Gazz. Chim. Ital., 105, p. 85; Grimaud, M., Pfister-Guillouzo, G., (1975) Org. Magn. Reson., 7, p. 386; Jin, O., Wildman, T.A., (1991) J. Phys. Chem., 95, p. 20; Baliah, V., Aparajithan, K., (1963) Tetrahedron, 19, p. 2177; Benassi, R., Iarossi, D., Folli, U., Schenetti, L., Taddei, F., (1981) J. Chem. Soc., Perkin Trans. 2, p. 228; Goethals, G., Uzan, R., Nadjo, L., Doucet, J.-P., (1982) J. Chem. Soc., Perkin Trans. 2, p. 885; Krueger, P.J., (1973) Can. J. Chem., 51, p. 1363; Mitzel, N.W., Smart, B.A., Blake, A.J., Robertson, H.E., Rankin, D.W.H., (1996) J. Phys. Chem., 100, p. 9339; Blake, A.J., Brain, P.T., McNab, H., Miller, J., Morrison, C.A., Parsons, S., Rankin, D.W.H., Smart, B.A., (1996) J. Phys. Chem., 100, p. 12280; Mitzel, N.W., Rankin, D.W.H., (2003) Dalton Trans., p. 3650; Kulhánek, J., Böhm, S., Palát Jr., K., Exner, O., (2004) J. Phys. Org. Chem., 17, p. 686; Zhao, Y., Truhlar, D.G., (2008) Acc. Chem. Res., 41, p. 157; Haworth, R.D., Jones, B., Way, Y.M., (1943) J. Chem. Soc., p. 10; Buděšínský, M., Kulhánek, J., Böhm, S., Cigler, P., Exner, O., (2004) Magn. Reson. Chem., 42, p. 844; Zeil, W., Haase, J., Wegmann, L., (1966) Z. Instrumentenkd., 74, p. 84; Bastiansen, O., Graber, R., Wegmann, L., (1969) Balzers High Vac. Rep., 23, p. 3224; Hinchley, S.L., Robertson, H.E., Borisenko, K.B., Turner, A.R., Johnston, B.F., Rankin, D.W.H., Ahmadian, M., Cowley, A.H., (2004) Dalton Trans., p. 2469; Ross, A.W., Fink, M., Hilderbrandt, R., Wilson, A.J.C., (1992) International Tables for Crystallography, 100, p. 245. , Kluwer Academic Publishers: Dordrecht, The Netherlands; Hehre, W., Radom, L., Schleyer V. P, R., Pople, J.A., (1986) Ab Initio Molecular Orbital Theory, , Wiley: New York; Frisch, M.J., Trucks, G.W., Schlegel, H.B., Scuseria, G.E., Robb, M.A., Cheeseman, J.R., Montgomery Jr., J.A., Pople, J.A., (2004) Gaussian 03, , revision C.02; Gaussian, Inc.: Wallingford, CT; Bühl, M., Unpublished resultsSipachev, V.A., (1985) J. Mol. Struct. (THEOCHEM), 121, p. 143; Sipachev, V.A., (2001) J. Mol. Struct., 567, p. 67

Keywords

Ab initio calculations
Anticlinal structure
Bond angle
Computational protocols
Diffraction analysis
Gas electron diffraction
Geometrical parameters
Long range correlations
Molecular shapes
Nonplanar conformation
Spectroscopic investigations
Steric crowding
Steric factor
Theoretical investigations
Torsional angle
UV spectrum
Conformations
Electron diffraction
Resonance
Ultraviolet spectroscopy
Bond length
2 methylacetophenone
acetophenone derivative
carbon
methyl group
oxygen
unclassified drug
ab initio calculation
article
carbon nuclear magnetic resonance
chemical bond
chemical reaction
chemical structure
conformation
dipole
electron diffraction
gas
reaction analysis
stereospecificity
structure analysis
ultraviolet spectroscopy

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10.1021/jo100291r

http://www.scopus.com/inward/record.url?eid=2-s2.0-77955156088&partnerID=40&md5=43efad44ef6ee6f1dc09bcfb344dcdfe

Cite this

@article{5f3ed44dba184e0d96ff7df6e8a03c75,

title = "Does 2-methylacetophenone comply with steric inhibition of resonance? A direct experimental proof of its nonplanar conformation from a joint ab initio/electron diffraction analysis",

abstract = "(Figure presented) The structure and conformations of 2-methylacetophenone (1) have been investigated by ab initio calculations carried out at the MP2(full)/6-311++G* level and by gas electron diffraction (GED). According to both methods, 1 exists predominantly as a form with the CεO bond synclinal with respect to the Car-C(O) bond (1B), with a torsional angle [C(6)-C(1)-CεO] of 32.7(24)° as determined by GED and 26.0° from MP2(full)/6-311++G. Calculations also predict the presence of a second conformer, the anticlinal structure (1C), with φ = 140.0°, with an abundance of less than 6%, an amount hardly detectable by GED. Different DFT computational protocols both support a nonplanar form of the predominant conformer (B2PLYP) and are in contradiction (B3LYP, M052x, B98, B97-D) with this experimental finding. The GED results, supported by the calculations that involve long-range correlation, are in a good agreement with 13C NMR spectroscopic investigations, UV spectra, and dipole moment studies. However, previous claims that assumed steric inhibition of resonance caused by a significantly nonplanar conformation with φ close to 90° have been disproved. Steric crowding is evident from the geometrical parameters, particularly from the C(1)-C(2) bond length and from the C(1)-C(2)-C(H 3) and C(2)-C(1)-C(O) bond angles. It is concluded that any explanation of reactivity by steric inhibition of resonance and by other steric factors must be supported by experimental and/or theoretical investigation of the actual molecular shape. {\textcopyright} 2010 American Chemical Society.",

keywords = "Ab initio calculations, Anticlinal structure, Bond angle, Computational protocols, Diffraction analysis, Gas electron diffraction, Geometrical parameters, Long range correlations, Molecular shapes, Nonplanar conformation, Spectroscopic investigations, Steric crowding, Steric factor, Theoretical investigations, Torsional angle, UV spectrum, Conformations, Electron diffraction, Resonance, Ultraviolet spectroscopy, Bond length, 2 methylacetophenone, acetophenone derivative, carbon, methyl group, oxygen, unclassified drug, ab initio calculation, article, carbon nuclear magnetic resonance, chemical bond, chemical reaction, chemical structure, conformation, dipole, electron diffraction, gas, reaction analysis, stereospecificity, structure analysis, ultraviolet spectroscopy",

author = "D. Hnyk and S. Samdal and O. Exner and D.A. Wann and D.W.H. Rankin",

note = "Cited By (since 1996):2 Export Date: 1 October 2013 Source: Scopus CODEN: JOCEA doi: 10.1021/jo100291r Language of Original Document: English Correspondence Address: Hnyk, D.; Institute of Inorganic Chemistry of the ASCR, v.v.i., No. 1001, CZ-250 68 Husinec-{\v R}e{\v z}, Czech Republic; email: [email protected] Chemicals/CAS: carbon, 7440-44-0; oxygen, 7782-44-7 References: Dippy, J.F.J., Hughes, S.R.C., Laxton, J.W., (1954) J. Chem. Soc., p. 1470; Wilson, J.M., Gore, N.E., Sawbridge, J.E., Cardenas-Cruz, F., (1967) J. Chem. Soc. B, p. 852; Charton, M., (1971) Prog. Phys. Org. Chem., 8, p. 235; Zalewski, R.I., Patai, S., (1992) The Chemistry of Functional Groups. Supplement B: The Chemistry of Acid Derivatives, 2. , Wiley: New York; Kukol, A., Strehle, F., Thielking, G., Gr{\"u}tzmacher, H.F., (1993) Org. Mass Spectrom., 28, p. 1107; Decouzon, M., Ertl, P., Exner, O., Gal, J.-F., Maria, P.-C., (1993) J. Am. Chem. Soc., 115, p. 12071; Decouzon, M., Exner, O., Gal, J.-F., Maria, P.-C., (1996) J. Chem. Soc., Perkin Trans. 2, p. 475; Decouzon, M., Gal, J.-F., Maria, P.-C., B{\"o}hm, S., Jim{\'e}nez, P., Roux, M.V., Exner, O., (1997) New J. Chem., 21, p. 561; Braude, E.A., Sondheimer, F., Forbes, W.F., (1954) Nature, 173, p. 117; Yates, K., Scott, B.F., (1963) Can. J. Chem., 41, p. 2320; Dhami, K.S., Stothers, J.B., (1965) Can. J. Chem., 43, p. 479; Guilleme, J., Diez, E., Bermejo, F.J., (1985) Magn. Reson. Chem., 23, p. 442; Oakley, M.G., Boykin, D.W., (1986) J. Chem. Soc., Chem. Commun., p. 439; Baumstark, A.L., Balakrishnan, P., Dotrong, M., McCloskey, C.J., Oakley, M.G., Boykin, D.W., (1987) J. Am. Chem. Soc., 109, p. 1059; Zaitsev, B.A., (1974) Izv. Akad. Nauk SSSR, Ser. Khim., p. 780; Lumbroso, H., Liegeois, C., Goethals, G., Uzan, R., (1983) Z. Phys. Chem., 138, p. 167; Smeyers, Y.G., Sieiro, C., (1979) Theor. Chim. Acta, 28, p. 355; B{\"o}hm, S., Exner, O., (2000) Chem.- Eur. J., 6, p. 3391; B{\"o}hm, S., Exner, O., (2001) New J. Chem., 25, p. 250; Tinant, B., Declercq, J.-P., Van Meerssch, M., Exner, O., (1988) Collect. Czech. Chem. Commun., 53, p. 301; Hnyk, D., Borisenko, K.B., Samdal, S., Exner, O., (2000) Eur. J. Org. Chem., p. 2063; Montaudo, G., Caccamese, S., Librando, V., Maravigna, P., (1975) Gazz. Chim. Ital., 105, p. 85; Grimaud, M., Pfister-Guillouzo, G., (1975) Org. Magn. Reson., 7, p. 386; Jin, O., Wildman, T.A., (1991) J. Phys. Chem., 95, p. 20; Baliah, V., Aparajithan, K., (1963) Tetrahedron, 19, p. 2177; Benassi, R., Iarossi, D., Folli, U., Schenetti, L., Taddei, F., (1981) J. Chem. Soc., Perkin Trans. 2, p. 228; Goethals, G., Uzan, R., Nadjo, L., Doucet, J.-P., (1982) J. Chem. Soc., Perkin Trans. 2, p. 885; Krueger, P.J., (1973) Can. J. Chem., 51, p. 1363; Mitzel, N.W., Smart, B.A., Blake, A.J., Robertson, H.E., Rankin, D.W.H., (1996) J. Phys. Chem., 100, p. 9339; Blake, A.J., Brain, P.T., McNab, H., Miller, J., Morrison, C.A., Parsons, S., Rankin, D.W.H., Smart, B.A., (1996) J. Phys. Chem., 100, p. 12280; Mitzel, N.W., Rankin, D.W.H., (2003) Dalton Trans., p. 3650; Kulh{\'a}nek, J., B{\"o}hm, S., Pal{\'a}t Jr., K., Exner, O., (2004) J. Phys. Org. Chem., 17, p. 686; Zhao, Y., Truhlar, D.G., (2008) Acc. Chem. Res., 41, p. 157; Haworth, R.D., Jones, B., Way, Y.M., (1943) J. Chem. Soc., p. 10; Bud{\v e}{\v s}{\'i}nsk{\'y}, M., Kulh{\'a}nek, J., B{\"o}hm, S., Cigler, P., Exner, O., (2004) Magn. Reson. Chem., 42, p. 844; Zeil, W., Haase, J., Wegmann, L., (1966) Z. Instrumentenkd., 74, p. 84; Bastiansen, O., Graber, R., Wegmann, L., (1969) Balzers High Vac. Rep., 23, p. 3224; Hinchley, S.L., Robertson, H.E., Borisenko, K.B., Turner, A.R., Johnston, B.F., Rankin, D.W.H., Ahmadian, M., Cowley, A.H., (2004) Dalton Trans., p. 2469; Ross, A.W., Fink, M., Hilderbrandt, R., Wilson, A.J.C., (1992) International Tables for Crystallography, 100, p. 245. , Kluwer Academic Publishers: Dordrecht, The Netherlands; Hehre, W., Radom, L., Schleyer V. P, R., Pople, J.A., (1986) Ab Initio Molecular Orbital Theory, , Wiley: New York; Frisch, M.J., Trucks, G.W., Schlegel, H.B., Scuseria, G.E., Robb, M.A., Cheeseman, J.R., Montgomery Jr., J.A., Pople, J.A., (2004) Gaussian 03, , revision C.02; Gaussian, Inc.: Wallingford, CT; B{\"u}hl, M., Unpublished resultsSipachev, V.A., (1985) J. Mol. Struct. (THEOCHEM), 121, p. 143; Sipachev, V.A., (2001) J. Mol. Struct., 567, p. 67",

year = "2010",

month = aug,

day = "6",

doi = "10.1021/jo100291r",

language = "English",

volume = "75",

pages = "4939--4943",

journal = "Journal of Organic Chemistry",

issn = "0022-3263",

publisher = "American Chemical Society",

number = "15",

}

TY - JOUR

T1 - Does 2-methylacetophenone comply with steric inhibition of resonance? A direct experimental proof of its nonplanar conformation from a joint ab initio/electron diffraction analysis

AU - Hnyk, D.

AU - Samdal, S.

AU - Exner, O.

AU - Wann, D.A.

AU - Rankin, D.W.H.

N1 - Cited By (since 1996):2 Export Date: 1 October 2013 Source: Scopus CODEN: JOCEA doi: 10.1021/jo100291r Language of Original Document: English Correspondence Address: Hnyk, D.; Institute of Inorganic Chemistry of the ASCR, v.v.i., No. 1001, CZ-250 68 Husinec-Řež, Czech Republic; email: [email protected] Chemicals/CAS: carbon, 7440-44-0; oxygen, 7782-44-7 References: Dippy, J.F.J., Hughes, S.R.C., Laxton, J.W., (1954) J. Chem. Soc., p. 1470; Wilson, J.M., Gore, N.E., Sawbridge, J.E., Cardenas-Cruz, F., (1967) J. Chem. Soc. B, p. 852; Charton, M., (1971) Prog. Phys. Org. Chem., 8, p. 235; Zalewski, R.I., Patai, S., (1992) The Chemistry of Functional Groups. Supplement B: The Chemistry of Acid Derivatives, 2. , Wiley: New York; Kukol, A., Strehle, F., Thielking, G., Grützmacher, H.F., (1993) Org. Mass Spectrom., 28, p. 1107; Decouzon, M., Ertl, P., Exner, O., Gal, J.-F., Maria, P.-C., (1993) J. Am. Chem. Soc., 115, p. 12071; Decouzon, M., Exner, O., Gal, J.-F., Maria, P.-C., (1996) J. Chem. Soc., Perkin Trans. 2, p. 475; Decouzon, M., Gal, J.-F., Maria, P.-C., Böhm, S., Jiménez, P., Roux, M.V., Exner, O., (1997) New J. Chem., 21, p. 561; Braude, E.A., Sondheimer, F., Forbes, W.F., (1954) Nature, 173, p. 117; Yates, K., Scott, B.F., (1963) Can. J. Chem., 41, p. 2320; Dhami, K.S., Stothers, J.B., (1965) Can. J. Chem., 43, p. 479; Guilleme, J., Diez, E., Bermejo, F.J., (1985) Magn. Reson. Chem., 23, p. 442; Oakley, M.G., Boykin, D.W., (1986) J. Chem. Soc., Chem. Commun., p. 439; Baumstark, A.L., Balakrishnan, P., Dotrong, M., McCloskey, C.J., Oakley, M.G., Boykin, D.W., (1987) J. Am. Chem. Soc., 109, p. 1059; Zaitsev, B.A., (1974) Izv. Akad. Nauk SSSR, Ser. Khim., p. 780; Lumbroso, H., Liegeois, C., Goethals, G., Uzan, R., (1983) Z. Phys. Chem., 138, p. 167; Smeyers, Y.G., Sieiro, C., (1979) Theor. Chim. Acta, 28, p. 355; Böhm, S., Exner, O., (2000) Chem.- Eur. J., 6, p. 3391; Böhm, S., Exner, O., (2001) New J. Chem., 25, p. 250; Tinant, B., Declercq, J.-P., Van Meerssch, M., Exner, O., (1988) Collect. Czech. Chem. Commun., 53, p. 301; Hnyk, D., Borisenko, K.B., Samdal, S., Exner, O., (2000) Eur. J. Org. Chem., p. 2063; Montaudo, G., Caccamese, S., Librando, V., Maravigna, P., (1975) Gazz. Chim. Ital., 105, p. 85; Grimaud, M., Pfister-Guillouzo, G., (1975) Org. Magn. Reson., 7, p. 386; Jin, O., Wildman, T.A., (1991) J. Phys. Chem., 95, p. 20; Baliah, V., Aparajithan, K., (1963) Tetrahedron, 19, p. 2177; Benassi, R., Iarossi, D., Folli, U., Schenetti, L., Taddei, F., (1981) J. Chem. Soc., Perkin Trans. 2, p. 228; Goethals, G., Uzan, R., Nadjo, L., Doucet, J.-P., (1982) J. Chem. Soc., Perkin Trans. 2, p. 885; Krueger, P.J., (1973) Can. J. Chem., 51, p. 1363; Mitzel, N.W., Smart, B.A., Blake, A.J., Robertson, H.E., Rankin, D.W.H., (1996) J. Phys. Chem., 100, p. 9339; Blake, A.J., Brain, P.T., McNab, H., Miller, J., Morrison, C.A., Parsons, S., Rankin, D.W.H., Smart, B.A., (1996) J. Phys. Chem., 100, p. 12280; Mitzel, N.W., Rankin, D.W.H., (2003) Dalton Trans., p. 3650; Kulhánek, J., Böhm, S., Palát Jr., K., Exner, O., (2004) J. Phys. Org. Chem., 17, p. 686; Zhao, Y., Truhlar, D.G., (2008) Acc. Chem. Res., 41, p. 157; Haworth, R.D., Jones, B., Way, Y.M., (1943) J. Chem. Soc., p. 10; Buděšínský, M., Kulhánek, J., Böhm, S., Cigler, P., Exner, O., (2004) Magn. Reson. Chem., 42, p. 844; Zeil, W., Haase, J., Wegmann, L., (1966) Z. Instrumentenkd., 74, p. 84; Bastiansen, O., Graber, R., Wegmann, L., (1969) Balzers High Vac. Rep., 23, p. 3224; Hinchley, S.L., Robertson, H.E., Borisenko, K.B., Turner, A.R., Johnston, B.F., Rankin, D.W.H., Ahmadian, M., Cowley, A.H., (2004) Dalton Trans., p. 2469; Ross, A.W., Fink, M., Hilderbrandt, R., Wilson, A.J.C., (1992) International Tables for Crystallography, 100, p. 245. , Kluwer Academic Publishers: Dordrecht, The Netherlands; Hehre, W., Radom, L., Schleyer V. P, R., Pople, J.A., (1986) Ab Initio Molecular Orbital Theory, , Wiley: New York; Frisch, M.J., Trucks, G.W., Schlegel, H.B., Scuseria, G.E., Robb, M.A., Cheeseman, J.R., Montgomery Jr., J.A., Pople, J.A., (2004) Gaussian 03, , revision C.02; Gaussian, Inc.: Wallingford, CT; Bühl, M., Unpublished resultsSipachev, V.A., (1985) J. Mol. Struct. (THEOCHEM), 121, p. 143; Sipachev, V.A., (2001) J. Mol. Struct., 567, p. 67

PY - 2010/8/6

Y1 - 2010/8/6

N2 - (Figure presented) The structure and conformations of 2-methylacetophenone (1) have been investigated by ab initio calculations carried out at the MP2(full)/6-311++G* level and by gas electron diffraction (GED). According to both methods, 1 exists predominantly as a form with the CεO bond synclinal with respect to the Car-C(O) bond (1B), with a torsional angle [C(6)-C(1)-CεO] of 32.7(24)° as determined by GED and 26.0° from MP2(full)/6-311++G. Calculations also predict the presence of a second conformer, the anticlinal structure (1C), with φ = 140.0°, with an abundance of less than 6%, an amount hardly detectable by GED. Different DFT computational protocols both support a nonplanar form of the predominant conformer (B2PLYP) and are in contradiction (B3LYP, M052x, B98, B97-D) with this experimental finding. The GED results, supported by the calculations that involve long-range correlation, are in a good agreement with 13C NMR spectroscopic investigations, UV spectra, and dipole moment studies. However, previous claims that assumed steric inhibition of resonance caused by a significantly nonplanar conformation with φ close to 90° have been disproved. Steric crowding is evident from the geometrical parameters, particularly from the C(1)-C(2) bond length and from the C(1)-C(2)-C(H 3) and C(2)-C(1)-C(O) bond angles. It is concluded that any explanation of reactivity by steric inhibition of resonance and by other steric factors must be supported by experimental and/or theoretical investigation of the actual molecular shape. © 2010 American Chemical Society.

AB - (Figure presented) The structure and conformations of 2-methylacetophenone (1) have been investigated by ab initio calculations carried out at the MP2(full)/6-311++G* level and by gas electron diffraction (GED). According to both methods, 1 exists predominantly as a form with the CεO bond synclinal with respect to the Car-C(O) bond (1B), with a torsional angle [C(6)-C(1)-CεO] of 32.7(24)° as determined by GED and 26.0° from MP2(full)/6-311++G. Calculations also predict the presence of a second conformer, the anticlinal structure (1C), with φ = 140.0°, with an abundance of less than 6%, an amount hardly detectable by GED. Different DFT computational protocols both support a nonplanar form of the predominant conformer (B2PLYP) and are in contradiction (B3LYP, M052x, B98, B97-D) with this experimental finding. The GED results, supported by the calculations that involve long-range correlation, are in a good agreement with 13C NMR spectroscopic investigations, UV spectra, and dipole moment studies. However, previous claims that assumed steric inhibition of resonance caused by a significantly nonplanar conformation with φ close to 90° have been disproved. Steric crowding is evident from the geometrical parameters, particularly from the C(1)-C(2) bond length and from the C(1)-C(2)-C(H 3) and C(2)-C(1)-C(O) bond angles. It is concluded that any explanation of reactivity by steric inhibition of resonance and by other steric factors must be supported by experimental and/or theoretical investigation of the actual molecular shape. © 2010 American Chemical Society.

KW - Ab initio calculations

KW - Anticlinal structure

KW - Bond angle

KW - Computational protocols

KW - Diffraction analysis

KW - Gas electron diffraction

KW - Geometrical parameters

KW - Long range correlations

KW - Molecular shapes

KW - Nonplanar conformation

KW - Spectroscopic investigations

KW - Steric crowding

KW - Steric factor

KW - Theoretical investigations

KW - Torsional angle

KW - UV spectrum

KW - Conformations

KW - Electron diffraction

KW - Resonance

KW - Ultraviolet spectroscopy

KW - Bond length

KW - 2 methylacetophenone

KW - acetophenone derivative

KW - carbon

KW - methyl group

KW - oxygen

KW - unclassified drug

KW - ab initio calculation

KW - article

KW - carbon nuclear magnetic resonance

KW - chemical bond

KW - chemical reaction

KW - chemical structure

KW - conformation

KW - dipole

KW - electron diffraction

KW - gas

KW - reaction analysis

KW - stereospecificity

KW - structure analysis

KW - ultraviolet spectroscopy

U2 - 10.1021/jo100291r

DO - 10.1021/jo100291r

M3 - Article

SN - 0022-3263

VL - 75

SP - 4939

EP - 4943

JO - Journal of Organic Chemistry

JF - Journal of Organic Chemistry

IS - 15

ER -