Evidence for twisted norbornanes. X-ray diffraction and valence force-field calculations

Altona, C.; Sundaralingam, M.

doi:10.1021/ja00710a036

Cited by 84 publications

(47 citation statements)

References 2 publications

Supporting

Mentioning

Contrasting

Unclassified

Order By: Relevance

“…Further work seems necessary to clarify this point. The torsion angles and the 'twisting' of the norbornyl fragment caused by steric effects of the sub- stituents have been discussed elsewhere (Altona & Sundaralingam, 1970) and are not treated here.…”

Section: Discussionmentioning

confidence: 99%

“…Comparison of experimental and calculated structures has been profitable. It was demonstrated that norbornanes and camphanes may adapt their geometry to strain induced by certain substituents by either of two possible modes of twist in which the entire skeleton takes part (Altona & Sundaralingam, 1970).…”

Section: (2) Vmentioning

confidence: 99%

“…Accurate structural data of a series of carefully selected norbornanes might provide a basis for understanding various factors governing the ground-state energy and geometry of these moderately strained and moderately 'flexible' compounds (Altona & Sundaralingam, 1970). …”

Section: Introductionmentioning

confidence: 99%

“…DT: Dallinga & Toneman, 1968;MKY: Morino, Kuchitsu & Yokozeki, 1967;CWB: Chiang, Wilcox & Bauer, 1968;FBK: Fratini, Britts & Karle, 1967;GS: Gleicher & Schleyer, 1967. * Mean of C(3)-C(4) and C(1)-C(6) distances; the remaining distances and angles are unreliable because of the disorder t Force field described by Altona & Sundaralingam, 1970 Triuranium pentaselenide, U3Ses, crystallizes with an orthorhombic unit cell ; ao = 12.43 (2), bo = 8"48 (1) and Co = 7.77 (1) A, Z= 4, space group probably Pnma. Two environmentally distinct types of uranium atom and two environmentally distinct types of selenium atom are found in the structure.…”

mentioning

confidence: 99%

See 3 more Smart Citations

Crystal and molecular structure of racemic 2-exo-norbornanol p-toluenesulfonate: a case of enantiomeric disorder

Altona¹,

Sundaralingam²

1972

Acta Crystallogr Sect B

Self Cite

View full text Add to dashboard Cite

The tosyl ester of racemic 2-exo-norbornanol (bicyclo[2.2.1]heptane-2-exo-ol p-toluenesulfonate), m.p. 54"5 °, crystallizes in the triclinic system: a = 6" 18 !, b = 11.092, c = 11-060 A, a = 111.4, fl = 103-6, 7 = 94"8 °, Z= 2. 2189 independent nonzero reflections were measured on a four-circle diffractometer (Cu Ka radiation), utilizing the 0-20 scan mode. Statistical tests indicate the centric space group P]. The structure was solved by the heavy-atom method. Full-matrix least-squares refinement reduced the R index to about 8 %, and convergence seemed complete. However, a difference synthesis revealed partial disorder of carbon atoms C(1), C(3), C(4), and C(6) of the norbornane moiety. The disordered atoms form a second, enantiomeric cage, sharing the 'non-disordered' atoms C(2), C(5) and C(7) with the original molecule. The crystal packing about the cage atoms appears sufficiently loose to permit a statistical disruption of the regular arrangement of L and D molecules, approximately 24% of L being replaced by D and vice versa. Further refinement proceeded to a final R index of 4.1%. Atomic distances are (uncorrected for thermal libration): (C-C) average aromatic ring=

show abstract

Section: Discussionmentioning

confidence: 99%

Section: (2) Vmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

mentioning

confidence: 99%

See 2 more Smart Citations

Crystal and molecular structure of racemic 2-exo-norbornanol p-toluenesulfonate: a case of enantiomeric disorder

Altona¹,

Sundaralingam²

1972

Acta Crystallogr Sect B

Self Cite

View full text Add to dashboard Cite

show abstract

“…The reaction between norcamphor, a bicyclic ketone of fixed geometry [2][3][4] , with amines of different basicity, was studied in order to evaluate the above-mentioned question.…”

Section: Introductionmentioning

confidence: 99%

The general mechanisms of attack of nitrogen nucleophiles on carbonyl compounds: facts that determine the change of the rate-pH profiles

Brighente¹,

Yunes²

1997

J. Braz. Chem. Soc.

View full text Add to dashboard Cite

Foi descrito um mecanismo geral para a etapa de ataque da reação de nucleófilos nitrogenados com compostos carbonílicos para formar intermediários de adição neutro. Este mecansimo geral está baseado na importância relativa do mecanismo "concertado" com respeito ao mecanismo "por etapas". O mecanismo "concertado" envolve o ataque da base nitrogenada ao composto carbonílico catalisado pelo íon hidrônio, enquanto que o mecanismo "por etapas" envolve a formação prévia de um intermediário tetraédrico zwiteriônico (T ± ), com posterior transferência de próton a partir do íon hidrônio. A importância relativa destes dois passos origina três diferentes tipos de perfis de velocidade em função do pH. A importância do mecanismo "por etapas" depende da estabilidade do intermediário T ± , que por sua vez depende do pKa do nucleófilo nitrogenado e da constante de equilíbrio (Kad) para a formação do intermediário neutro (T 0 ). A comparação entre as reações de p-clorobenzaldeído e norcanfor com diferentes nucleófilos nitrogenados mostra que o mecanismo geral depende de cada tipo de composto carbonílico. Isto deve-se a dois fatos: A grande influência dos efeitos estéricos e eletrônicos na estrutura dos compostos carbonílicos, e o fato de que o valor do pKa do nucleófilo nitrogenado é o fator mais importante na predição dos perfis. O pKa do nucleófilo nitrogenado está mais relacionado com a estabilidade do intermediário T ± que de T 0 , enquanto que o valor de Kad está relacionado apenas com a estabilidade do intermediário T 0 .It have been described a general mechanism for the attack step of the reactions between nitrogen nucleophiles and carbonyl compounds to form a neutral tetrahedral addition intermediate. This general mechanism is based on the relative importance of the "concerted" hydronium-ion catalyzed attack of the nitrogen base on the carbonyl compound with respect to the "step wise" mechanism that involves the previous formation of a zwitterionic tetrahedral intermediate (T ± ) and the posterior proton transfer to it from the hydronium-ion. The relative importance of this pathway gives origin to three kinds of profile rates vs pH for these reactions. On the other hand, the importance of the "stepwise" mechanism was attributed to a dependence on the stability of the T ± intermediate that is related to the pKa of the nitrogen base and the Kad (the equilibrium constant for the formation of the neutral tetrahedral addition intermediate (T 0 )). The comparison of the reactions of p-chlorobenzaldehyde and norcamphor with different nitrogen nucleophiles led to the observation that the general mechanism depends on each type of carbonyl compound. This is due to the great influence of the steric and electronic effects of the compound's structure, and the fact that the pKa value of the nitrogen base, which is more related to the stability of the T ± than the T 0 intermediate, is more important as a factor of prediction of the profiles than the value of Kad, this value being more related to the stability of the T 0 intermediate.

show abstract

Azabrendanes. I. Synthesis, structure and spectral parameters of N-(arylsulfonyl)-exo-2-hydroxy-4-azatricyclo[4.2.1.03,7]nonanes

et al. 1997

View full text Add to dashboard Cite

Evidence for twisted norbornanes. X-ray diffraction and valence force-field calculations

Cited by 84 publications

References 2 publications

Crystal and molecular structure of racemic 2-exo-norbornanol p-toluenesulfonate: a case of enantiomeric disorder

Crystal and molecular structure of racemic 2-exo-norbornanol p-toluenesulfonate: a case of enantiomeric disorder

The general mechanisms of attack of nitrogen nucleophiles on carbonyl compounds: facts that determine the change of the rate-pH profiles

Azabrendanes. I. Synthesis, structure and spectral parameters of N-(arylsulfonyl)-exo-2-hydroxy-4-azatricyclo[4.2.1.03,7]nonanes

Contact Info

Product

Resources

About