E.V. Van Den Berghe

A study of the chemical bond in (CH3)nSn(SCH3)4−n (n=0, 1, 2, 3) by nmr (1H, 119Sn, 13C) spectroscopy

Abstract The 119 Sn and 13 C NMR spectra of (CH 3 ) n Sn(SCH 3 ) 4− n ( n =0, 1, 2, 3) compounds are presented. From the observed chemical shifts and by comparison with other groups of compounds, inductive and magnetic anisotropy effects seem to govern the shifts of the nuclei studied.

The proton magnetic resonance spectra and electrical dipole moments of methyltin halides

Abstract The PMR spectra and electric moments of (CH 3 ) n SnX 4− n compounds have been studied for X = Cl, Br and I. The trend of the chemical shifts is opposite to the inductive effect of the substituent, X, and can be explained by a diamagnetic anisotropy effect acting along the SnX bond. Also, the SnCH coupling constants do not agree with any additivity rule as a function of progressive halogenation, the deviations being higher for chlorides than for bromides or iodides. This has been ascribed to a strong distortion of the atomic orbitals of tin, increasing with electronegativity of the substituent. The eIectric moments can be explained by assuming resonance structures with a double-bond character in the SnX or the SnC bond.

A 29Si and 1H NMR study of (CH3)4-n SiXn compounds with X N(CH3)2, OCH3 and SCH3

Abstract The 1H and 29Si NMR spectra of (CH3)4−n SiXn compounds (X  N(CH3)2, OCH3 and SCH3) have been studied. The 29Si resonance shows an upfield shift with X  N(CH3)2, OCH3, and n = 2, 3, 4. This can be accounted for by increasing SiO and SiN back donation. Van der Waals interactions are proposed to explain certain NMR parameters. A linear correlation has been found between the 13CH coupling constants and the product of the electronegativity and Van der Waals radius in the (CH3)3 SiX compounds. This provides an explanation of the lower 13CH coupling constants of (CH3)3SiOCH3 and (CH3)3SiN(CH3)2 compared with those in Si(CH3)4.

A study of the structure of trimethyl-tinhaloacetates by N.M.R. and I.R. spectroscopy☆

Abstract The p.m.r. IR spectra of trimethyltinchloro-and-fluoroacetates have been studied. It could be established that these compounds in the solid state most probably are of a polymeric structure with five coordinated tin. In solution however, the molecules are mainly monomeric and tetragonal, but also some associated species must be present for the dichloro-, trichloro-, and trifluoroacetate. In the case of the monochloro- and dichloroacetate also the existence of rotational isomers could be established.

CNDO/2 study of 29Si NMR chemical shifts

Abstract A CNDO-2 study of 29 Si NMR chemical shifts for compounds of the type (CH 3 ) n SiX 4- n (X = H, F, Cl) is reported. The paramagnetic screening constants σ p are given. The general variation in σ p with n agrees fairly well with the variation of the observed chemical shifts for X = H and F, but the correlation is not so good for X = Cl.

Substitution effect of or (R = CH3, C2H5) groups on the 119Sn and 1H NMR spectra of (CH3)4-nSn(OR)n compounds;m evidence for a polymeric structure

Abstract We investigated the 1H and 119Sn NMR spectra of (CH3)4-nSn(OR)n (n = 1, 2, 3; R = CH3, C2H5) compounds. The different NMR parameters could not be interpreted with the aid of normal substitution effects based upon electronegativity considerations of the substituents. However, structural changes caused by polymerization could provide a rational explanation of the special NMR behaviour of these compounds.

A study of the 1H and 119Sn NMR spectra of (CH3)4−nSn(NR2)n compounds (RCH3, C2H5)

Abstract The 1 H and 119 Sn NMR spectra of the aminostannanes, (CH 3 ) 4− n Sn(NR 2 ) n (RCH 3 and C 2 H 5 ; n = 1−4) have been studied. The previously undetected 117,119 SnNCH coupling in the methylaminostannanes was observed in these experiments thus making the proposal of a fast exchange of amine groups made by other authors difficult to sustain. From consideration of the 119 Sn chemical shifts and the coupling constants 117,119 SnCH, 117,119 SnNCH, it has been shown that back-donation from the nitrogen lone pair to the vacant d orbitals of Sn is of little or no importance. On the other hand a significant intermolecular association via NH bridges apparently occurs in solutions of (CH 3 ) 3 SnN(CH 3 ) 2 and (CH 3 ) 2 Sn[Sn[N(CH 3 ) 2 ] 2 . It is suggested that weaker van der Waals interactions than these occur in other (CH 3 ) 4− n SnX n compounds which contain bulky X substituents and that these interactions explain the low 117,119 SnCH coupling constants of the compounds studied. The percentage s character is both Sn→CH 3 and Sn→NR 2 orbitals increases with increasing NR 2 substitution. The percentage s character increases in the SnCH 3 orbitals in the order N(CH 3 ) 2 >N(C 2 H 5 ) 2 while a corresponding decrease occurs in the Sn→NR 2 orbitals with the same substitution sequence.

Alkyl redistribution reactions of (CH3)nSnX4−ncompounds (X = CI, Br, I)

Abstract Redistribution reactions were studied by PMR methods for mixtures of Sn(CH 3 ) 4 with SnX 4 (X = CI, Br, I), for different molar ratios. Reaction mechanisms were proposed and could be confirmed by studying other mixtures containing, apart from the starting material, also one of the reaction products (CH 3 ) n SnX 4− n . The rate of redistribution decreases in the sequence: chlorides > bromides > iodides.

An investigation of the chemical behaviour in binary systems (CH3)4−nSnXn/(CH3)4−nSn(SCH3)n (X = Cl, Br, I) by 1H and 119Sn NMR

Abstract Binary systems of type (CH 3 ) 4− n SnX n / (CH 3 ) 4− n Sn (SCH 3 ) n (X = halogen, n = 1, 2, 3, 4) have been investigated in solution by 1 H and 119 Sn NMR spectroscopy At room temperature the existence of a rapid exchange of the halogen and SCH 3 substituents on the methyltin moiety was established, the rate of exchange being slowest with iodine; Low-temperature measurements provide additional evidence for the proposed exchange mechanism.

The vibrational spectra of trimethyl(methylthio)stannane and -germane

Abstract The IR and Raman spectra of trimethyl(methylthio)germane and -stannane have been measured. Vibrational assignments are proposed, based on characteristic group frequencies and Raman polarization data.