Planar structure isomers

Four-coordinate complexes provide good examples of the early use of preparative methods for establishing stereochemistry. For complexes of the type [Ma2b2], where a and b are unidentate ligands, a tetrahedral structure cannot produce isomerism whereas a planar structure leads to cis and trans isomers (see below). The preparation of 2 isomers of [PtCl2(NH3)2], for instance, was taken as good evidence for their planarity. ... 

The (Z)-isomers do not show a clear sequence (Table 7-2). This result is consistent with a planar structure for the ( >diazoates and a nonplanar, sterically hindered structure for the (Z)-diazoates, which is an obvious cause for their lower chemical stability. 

A hexagonal planar structure was once proposed for the [CrCl3(NH3)3] complex. Use the fact that only two isomers of the complex are known to rule out the hexagonal planar structure. 

The initial results on the [NaA ] clusters have been extended to the heterocyclic ring species [XAls] (X = Si, Ge, Sn, Pb) bearing a single charge and as a result are not prone to dissociation of an electron like the [Al4] or [Ga4H2] anions [69]. A planar four-membered ring structure is in all cases the most stable structural isomer with Al—Al distances in the range 2.57-2.61 A. 

Square planar structures can show cis-trans isomerism. Examples are drawn following, with the m-isomer drawn on the left, and the /ra/w-isomer drawn on the right. 

This type of conjugation is also possible if an atom with a lone pair of electrons is connected to an sp2 center, because once again the planar structure is stabilized by resonance. Such molecules give rise to E and Z isomers as shown in Scheme 5. (The asterisk in Scheme S and in 1 and 2 indicates the lone pair in the orbital at a right angle to the plane of the paper.)... 

In the lower triplet state, the silabenzene molecule retains its planar structure whose energy is higher by 107 kcal/mol than that of the structure of the singlet ground state (STO-3G) (78JA6499). Like benzene, silabenzene is more stable than its isomers (259)—(262) by, respectively, 38.4,... 

Abstract. We present a quantum-classieal determination of stable isomers of Na Arii clusters with an electronically excited sodium atom in 3p P states. The excited states of Na perturbed by the argon atoms are obtained as the eigenfunctions of a single-electron operator describing the electron in the field of a Na Arn core, the Na and Ar atoms being substituted by pseudo-potentials. These pseudo-potentials include core-polarization operators to account for polarization and correlation of the inert part with the excited electron . The geometry optimization of the excited states is carried out via the basin-hopping method of Wales et al. The present study confirms the trend for small Na Arn clusters in 3p states to form planar structures, as proposed earlier by Tutein and Mayne within the framework of a first order perturbation theory on a "Diatomics in Molecules" type model. 

Problem 9.18 Write planar structures for optical isomers of cu-2-chlorocyclohexanol. Indicate chiral C s. ... 

Problem 9.23 The planar structure of c -l,2-dimethylcyclohexane, which is meso, shows a plane of symmetry [Problem 9.4(e)). (a) Is the chair conformer achiral (f>) Why is this isomer optically inactive -4... 

Similar pairs of isomers of compounds of nickel as well as of palladium and of platinum with other groups have also been obtained.8 The x-ray study of crystalline potassium nickel dithio-oxalate9 has shown it to be isomorphous with the palladium and platinum compounds and has provided a detailed verification of the planar structure... 

PA Td structural isomers of each compound the planar isomers isomerize to Td ones at room temp. ... 

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