摘要:

Spectroscopists have often assumed, based only on the UV spectrum of the anilinium ion (NH3+), that ammonium groups cannot bring a “mesomeric” effect upon π systems. This assumption(1–3)which could be justified for the anilinium ion itself, whose OO band of the secondary transition (towards 260 nm) is very weak, has been unduly extended to all the ammonium groups. Actually, the interaction between a π system and (NXaXbXc)+groups has been studied by several authors(4–8)and we have shown that contrary to what had been assumed by spectroscopists, such an interaction induces strong effects on the UV spectrum of the benzene chromophore(9–11). Using the MNDO and the CNDO methods, we have studied the quantum factors which play a part in the long range interaction, between: an ω group X on the one hand, N on the other hand, and then , in NH2+CH2X, NH+(CH2Xa) CH2Xband NH+(C2H4)2X.

ISSN:0038-7010    

DOI:10.1080/00387018908053938

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

Dear Sir:

ISSN:0038-7010    

DOI:10.1080/00387018908053939

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

Hyperconjugation is not restricted to alkyl groups(1–4)and ammoniums interact with π systems through σ-π hyperconjugative coupling(5–9). Their influence on the UV spectrum of the secondary transition of the benzene chromophore in anilinium ions has only been studied during the last years. Previously it was assumed without enough experimental support, that ammonium groups have no spectroscopic effects on a π chromophore (for example:(10,11)). In fact, although it is a strong σ-electronwithdrawing substituent, an ammonium group is a π-donating one5–8). Its π-donating ability - contrary to what is observed in the corresponding alkyl groups where N is replaced by C - increases whenever the number of N+−C bonds increases, and −N(CH3)3+ could be as much π-donating as the −C(CH3)3group for pseudo-free molecules(5).

ISSN:0038-7010    

DOI:10.1080/00387018908053940

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

Retro Diels-Alder mechanism is the main fragmentation pattern of the 7-chloro Pyrano oxazine (2),7-morpholino pyrano oxasine (3),5-morpholino carbonyl-4-oxo-3-substituted phenyl-2-thio-1-3-oxazine-6-ylacetomorpholide (4) and ethyl-6-ethoxy carbonyl methyl-4-oxo-3-(substituted phenyl)-2-thio-2H-1,3-oxazine-5-carboxylate (5). Further fragmentation routes were also discussed.

ISSN:0038-7010    

DOI:10.1080/00387018908053941

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

The uranium concentrations of the natural water samples collected from Northern Aegean Region, were measured by laser-excited fluorescence technique for hydrogeochemical prospecting. The reconnaissance survey measurements were made using external standards and detailed analysis realised with internal standard method to correct the quenching. Uranium concentrations for waters of all types range from below the detection limit of 0.05 ppb to 309.09 ppb and have a mean of 16.07 ppb. The precision of the method as shown by standard deviation is satisfactory. The laser-induced fluorescence method was applied easily and successfully in the uranium prospecting program and the data might indicate a uranium deposite in Saricaoglu Region.

ISSN:0038-7010    

DOI:10.1080/00387018908053942

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

The1H NMR spectra of the potent anti-hypertensive drug, lofexidine,1, have been studied in CDCl3at 60 and 300 MHz. Both the achiral shift reagentr tris (6,6,7,7,8,8,8-heptafluoro-2,2-dimethyl-3,5-octanedionatol-europium(III),2and the chiral reagents1 tris[3-(heptafluoropropylhydroxymethylenel-d-camphoratoleuropium(III),3and tris[3-(trifluoromethylhydroxymethylenel-d-camphoratoleuropium(III),4, were employed. Substantial lanthanide induced shifts were observed with2,3or4, with the largest shifts seen for the methine at the chiral centerr followed by the signal of the NH. Enantiomeric shift differences for the CH3signal of1were seen with3OK4, with4inducing larger values of potential analytical utility. Using a non-racemic sample of1, the (-) enantiomer was shown to have a downfield sense of magnetic nonequivalence for the methyl resonance in the presence of added4.

ISSN:0038-7010    

DOI:10.1080/00387018908053943

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

Vibrational spectra have been published and normal coordinate calculations have been made for 1,2-dichlorobutane.1,2Those calculations were limited to the three conformers that had all four carbon atoms coplanar. Molecular mechanics calculations have now shown a conformer that was omitted to be the second most abundant conformer. Therefore, normal coordinate calculations have been made for this conformer and molecular mechanics calculations have been made for all possible conformers.

ISSN:0038-7010    

DOI:10.1080/00387018908053944

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

The mechanism of chemiluminescence in the reaction N + CO → NCO (1) and the electronic spectrum of NCO radical have been investigated by means of MINDO/3 CI method. The potential energy curves for the ground and some excited doublet and quartet states have been built along the linear and nonlinear (angle NCO is equal to 150°) reaction coordinates. The reaction channels N(4S) + CO(1σ+), N(2D) + CO(1°+) and N(2P) + CO(1σ+) have been discussed in detail. The spin-orbit coupling (SOC) constants for2π states and nonadiabatic SOC matrix elements <4σ−|;HSOC|X2π> have been calculated.

ISSN:0038-7010    

DOI:10.1080/00387018908053945

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

water proton T1 in blood from healthy volunteers and patients with acute leukaemia, lymphoma; iron deficiency anaemia, post hepatitic cirrhosis and tuberculosis, was measured by a FT-NMR spectrometer. Relaxation measurements were performed at 60MHz frequency and a temperature of (20 ± 0.5)C. The T1 measured for each disease correlates strongly with hemoglobin content. The spin-lattice relaxation time in each abnormal group was signaficantly (p < 0.001) elevated over normal group. There is little overlap between the healthy and abnormal groups. On the contrast, T1 ranges obtained for malignant groups and non-malignant diseases do overlap.

ISSN:0038-7010    

DOI:10.1080/00387018908053946

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

The IR spectra of the linkage isomers [Pd(bipy)(SCN)2] and [Pd(bipy)(NCS)2] have been determined in the C≡N stretching region (2200–2000 cm−1) and below 500 cm−1. The band shifts resulting from deuteration of the 2,2′-bipyridine (bipy) ring and15NCS-labelling are shown to provide a ready means for distinguishing between the internal ligand modes, the μPd-N(bipy) and μPd-SCN/μPd-NCS vibrations. The assignment technique has been further extended to the complexes [Pt(bipy)(SCN)2] and [Pd(phen)(SCN)2] (phen = 1,10-phenanthroline). Finally, a comparison between the IR spectra of [Pd(bipy)(NCO)2], [Pd(bipy)(NCS)2] and [Pd(bipy)(SCN)2] reveals that the frequencies μM-NCO, μM-NCS and μM-SCN decrease in the sequence NCO > NCS > SCN.

ISSN:0038-7010    

DOI:10.1080/00387018908053947

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor