首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献,搜索用时 0 毫秒
1.
Two structures have been proposed for humulinone (II and III in Fig. 1). The high resolution NMR spectrum of this and related substances points to the five-membered ring structure II.  相似文献   

2.
3.
4.
The structure of N2-sulphonylformamidines has been investigated by means of IR, 1H and 13CNMR spectroscopy. The compounds are shown to exist as two rotamers in solution. A previous report on the isolation of Z and E isomers (regarding the CN2-bond) for one N2-methane-sulphonylformamidine is shown to be dubious, the spectroscopical data indicating the two isomers to be rotamers at the C-N1 -bond.  相似文献   

5.
6.
7.
8.
Microwave spectra of phenylisocyanide,
(I), 2-D-phenylisocyanide, 2,4-D2-phenylisocyanide, and 2,4,6-D3-phenylisocyanide were recorded and analyzed. Assuming the structural identity of the C6H(3)H(4)H(5) fragments of I and of phenylcyanide (II). A C(1)-N distance of 1.410 Å and an
distance of 1.142 Å followed. The effects of changing some of the assumptions are discussed.  相似文献   

9.
The 13C NMR spectrum of dithizone, unlike that of its oxygen analogue, shows only five different types of carbon atom. The 13C chemical shift of the C?S group in dithizone is only 7 ppm to lower field of that of the C?O moiety in its analogous compound. The results can be rationalized by consideration of tautomeric equilibria which lead to C2v time-averaged symmetry.  相似文献   

10.
The dimeric indole alkaloid callichiline ( 2 ), C42H48O5N4, has been isolated from Callichilia (Hedranthera) barteri (HOOK . f.) PICHON along with vobtusine ( 1 ) and beninine ( 3 ). Its chemical reactions and spectral properties have shown that callichiline is made up of the same two monomeric ‘halves’ as vobtusine, that is beninine ( 3 ) and the vincadifformine analogue of beninine.  相似文献   

11.
In order to advance the studies of radiation graft copolymerization, we have presented the theory of coupling graft copolymerization and apply it to the investigation of the grafting of methylmethacrylate on to pre-irradiated polystyrene.  相似文献   

12.
13.
N.L. Allinger  J.T. Sprague 《Tetrahedron》1973,29(23):3811-3812
Molecular mechanics calculations on cycloheptadiene indicate that the molecule has a structure which undergoes a wide pseudorotational motion between two C1 forms, and a C1 form, and this structure is in equilibrium with the C2 form. It is shown that this equilibrium mixture is consistent with all of the available experimental data.  相似文献   

14.
The icosahedral quasicrystal structure is derived with local symmetry operations. Calculated Fourier transforms are compared with electron diffraction patterns. It is proposed that the structure building operations are models for the crystal growing process.  相似文献   

15.
16.
In the crystal structure of purine the molecules are linked together by single hydrogen bonds. The tautomer present has a proton linked to N(7) and not to N(9). Calculations indicate that the two tautomers have equal stabilities but that the N(7)H tautomer has a dipole moment much greater than the N(9)H one. The driving force for the presence of the N(7)H tautomer in the purine crystal is the greater electrostatic interaction energy obtained with this tautomer with respect to the one which would be obtained with the N(9)H one.
Zusammenfassung Der Purinkristall besteht aus der tautomeren Form des Moleküls, bei dem ein Proton am N(7) und nicht am N(9) gebunden ist. Die Rechnungen ergeben für beide tautomere Formen dieselbe Stabilität, aber das Dipolmoment der Form N(7)H ist wesentlich größer, als das der tautomeren Form N(9)H. Auch aus dem höheren Wert der elektrostatischen Wechselwirkungsenergie der Form N(7)H kann auf die Anwesenheit dieser Form im Kristall geschlossen werden.

Résumé Le cristal de la purine contient la forme tautomère de la molécule dans laquelle un proton est fixé sur N(7) et non sur N(9). Les calculs montrent que les deux formes tautomères ont la même stabilité mais que le moment dipolaire du tautomère N(7)H est nettement plus grand que celui du tautomère N(9)H. La présence du tautomère N(7)H dans le cristal peut alors être attribuée à la plus grande valeur de l'énergie d'interaction électrostatique par rapport à celle qui serait obtenue avec le tautomère N(9)H.
  相似文献   

17.
18.
19.
Results of a Fourier transform-ion cyclotron resonance study are reported concerning the reactivity of protonated perdeuteromethane and deuteronated methane, generated under varying pressure conditions in an external chemical ionization ion source, toward ammonia. The competition between proton and deuteron transfer from both protonated perdeuteromethane and deuteronated methane to ammonia exhibits chemically distinguishable hydrogens. The chemical behavior of protonated methane appears to be compatible with the theoretically predicted stable structure with CS symmetry, involving a three-center two-electron bond associating two hydrogens and the carbon atom. Interconversion of this structure due to exchange between one of these hydrogens and one of the three remaining hydrogens appears to be a fast process that is induced by interactions with the chemical ionization gas.  相似文献   

20.
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号