ISSN:0030-4921    

DOI:10.1002/mrc.1270020302

出版商:John Wiley&Sons Limited    

年代:1970

数据来源: WILEY

摘要:

AbstractThe19F NMR spectra of thecis‐ (1) and thetrans‐isomer (2) of the 1,2‐dichlorotetrafluorocyclopropane and that of the 1,1‐dichlorotetrafluorocyclopropane (3) have been investigated at different temperatures and in several solvents.From chemical shift calculations the two geminal fluorines in thecis‐isomer (1) could be assigned and on this basis the two vicinal coupling constants of1,Jtrans(ca.140°) andJcis(ca.0°), were unequivocally distinguished. By frequency sweep double resonanceJtranshas been shown to be of opposite sign toJgem, whereas forJcisthe situation has been found to be reversed. ThereforeJtransis presumably negative andJcispositive. Only the N(Jcis+Jtrans) value could be extracted from the vicinal coupling constant in the fragment CFClCFCl could be evaluated. It has been noted thatJcisis more sensitive to changes in temperature than isJtrans. The variations ofJcisandJtransinduced by solvents are, on the contrary, small and irregular and no correlation with the dielectric constant of the medium has been noted. The different temperature dependence ofJcisandJtranscan be useful for assigning the vicinal FF coupling constants in cyclopropane derivatives and also for defining their signs. This method was applied to the coupling constants extracted from the13C satellite spectrum of isomer3. The coupling constants results were compared with some literature data already known, and some rationalisation and correlations from the t

ISSN:0030-4921    

DOI:10.1002/mrc.1270020303

出版商:John Wiley&Sons Limited    

年代:1970

数据来源: WILEY

摘要:

AbstractUn certain nombre d'alcoylidène‐5 alcoyl‐2 dioxannes‐1,3 ont été étudiés par RMN. L'analyse des spectres permet de conclure à une conformation chaise prédominante de ces dérivés, le substituant alcoyle sur carbone 2 se plaçant en position équatorial. Pour les alcoylidène‐5 dioxannes‐1,3 non substitués sur carbone 2 il y a inversion rapide du cycle avec une barrière énerg

ISSN:0030-4921    

DOI:10.1002/mrc.1270020304

出版商:John Wiley&Sons Limited    

年代:1970

数据来源: WILEY

摘要:

AbstractA useful method for the assignment of hydroxyl groups in steroids is described in which hydroxy‐steroids are reacted with trifluoroacetic anhydride. The δ‐values of the CF3signals from the resulting trifluoroacetates characterize the positions of the trifluoroacetylated hydroxyl gr

ISSN:0030-4921    

DOI:10.1002/mrc.1270020305

出版商:John Wiley&Sons Limited    

年代:1970

数据来源: WILEY

摘要:

AbstractProton magnetic resonance spectra at 60 MHz are reported for 9, 9′‐biphenanthryl, 1‐phenylfluoranthene, 9‐benzylphenanthrene, 1‐, 4‐ and 9‐phenylphenanthrenes and 9‐methyl‐10‐phenylphenanthrene, all in CS2solution. Approximate values of some of the chemical shifts and coupling constants were extracted from the overlapped and often collapsed AB, ABC ABCD and AA′BB′C (phenyl) spin systems. By comparison with data for phenanthrene itself, estimates have been made for the dihedral angle, θ, between the planes of the phenyl ring and the phenanthrene nucleus in phenylphenanthrenes. These lead, except for 9‐phenylphenanthrene for which the angle derived from H(10) by PMR is higher than UV suggests, to plausible values for θ: 90°, 75°, 40° and 45 to 60°, for 4‐phenyl, 9‐methyl‐10‐phenyl‐, 1

ISSN:0030-4921    

DOI:10.1002/mrc.1270020306

出版商:John Wiley&Sons Limited    

年代:1970

数据来源: WILEY

摘要:

AbstractAn einer Anzahl vonN,N‐Dialkylaminoboranen wurde die Substituentenabhängigkeit der Rotationsbarriere um die NB‐Bindung mit Protonenresonanzen studiert. Dabei konnte (1) eine deutliche Abhängigkeit der Barriere von der Größe der Substituenten festgestellt werden, die auf eine ‘sterische Behinderung der Mesomerie’ zurückgeführt wird, und (2) eine z.T. außerordentlich große Erleichterung der Rotation, wenn Alkylgruppen am Bor durch ein Chlor bzw. eine zweite Aminogruppe substituiert werden. Die Erniedrigung der Rotationsbarriere umca.10 kcal/Mol in Bis‐aminoverbindungen verglichen mit den entsprechenden Monoaminoverbindungen wird durch eine Verminderung des Doppelbindungsgrades jeder NB‐Bindung infolge Beteiligung zweier N‐Atome an der Mesomerie des Grundzustandes erklärt. Dieser Effekt ist bei der Aminogruppe weit grö

ISSN:0030-4921    

DOI:10.1002/mrc.1270020307

出版商:John Wiley&Sons Limited    

年代:1970

数据来源: WILEY

摘要:

AbstractThe effect of aromatic and non‐aromatic solvents on the proton chemical shifts of 23 polar compounds has been determined. The protons which are activated by electron‐withdrawing groups show large highfield shifts in benzene (relative to the isotropic solvents). Based on evidence provided by infrared data, the highfield shifts of the acidic protons in benzene solution are interpreted in terms of a model involving CHπ hydrogen bonding. This model successfully interprets the data reported previously for steroidal ketones. The same model can be extended to benzene solutions of other polar compounds containing strongly electron‐deficient sites to which alkyl groups are attached. It is observed that the use of CCl4as a reference solvent in studies of benzene induced shifts may have greater significance, since these two solvents have similar dielectric c

ISSN:0030-4921    

DOI:10.1002/mrc.1270020308

出版商:John Wiley&Sons Limited    

年代:1970

数据来源: WILEY

摘要:

AbstractRotational barriers in 21p‐ andm‐substitutedN,N‐dimethylbenzamides in CDCl3as solvent have been determined using the intensity ratio method of Woodbrey. These data compare very well with values from the literature1obtained with a total line shape analysis. From structure‐reactivity correlations evidence has been obtained for a relatively strong resonance interaction between the substituent in the aromatic ring and the partially double ami

ISSN:0030-4921    

DOI:10.1002/mrc.1270020309

出版商:John Wiley&Sons Limited    

年代:1970

数据来源: WILEY

摘要:

AbstractVariable temperature fluorine magnetic resonance spectra have been obtained for 1‐fluorocyclooctene. At low temperatures both the processes of ring inversion and pseudorotation are slow on the NMR time scale, and two distinguishable conformations can be observed with a free energy difference of 95 cal/mole and a fluorine chemical shift difference of 6·7 ppm. A process with a free energy of activation of 6·1 kcal/mole interconverts the two conformati

ISSN:0030-4921    

DOI:10.1002/mrc.1270020310

出版商:John Wiley&Sons Limited    

年代:1970

数据来源: WILEY

摘要:

AbstractA study is reported on the chemical shift non‐equivalence of the diastereotopic protons at C‐4 in identically 3,3‐disubstituted β‐lactams having an asymmetric carbon atom in positions ranging from β to ε of the chain attached to the nitrogen atom. The non‐equivalence has been correlated with the nature of the substituents bonded to the chiral centre and to its distance from the

ISSN:0030-4921    

DOI:10.1002/mrc.1270020311

出版商:John Wiley&Sons Limited    

年代:1970

数据来源: WILEY