Planar structure

In the gold(lll) halides (except the fluoride) there is evidence for the formation of double molecules, AujXg (cf. chlorides of iron(III) and aluminium) so that the coordination is brought up to four, but with a planar structure ... 

The planar structure of thiazole (159) implies for the molecule a Cj-type symmetry (Fig. 1-8) and means that all the 18 fundamental vibrations are active in infrared and in Raman spectroscopy. Table 1-22 lists the predictions made on the basis of this symmetry for thiazole. 

The graphic that opened this chapter IS a molecular model of phenol that shows its planar structure and electro static potential... 

Azetidine itself has been studied by electron diffraction, which reveals a non-planar structure (Figure 1) (73CC772). The enhanced length of the bonds reflects the strain in the ring and the angle between the CCC and CNC planes of 37° is similar to that found for cyclobutane (35°), but quite different from that for oxetane (4°). 

Figure 1 Planar structure assumed for ellipsometric analysis is the complex index of...

These two energies are, respectively, comparable to the experimental activation energies for conformation inversion of the tub conformer and bond shifting, suggesting that the two planar structures represent the transition states for those processes. 

EPR studies and other physieal methods have provided the basis for some insight into the detailed geometiy of radieal species.Deduetions about strueture ean also be drawn from the study of the stereoehemistiy of reactions involving radical intermediates. Several structural possibilities must be considered. If discussion is limited to alkyl radicals, the possibilities include a rigid pyramidal structure, rapidly inverting pyramidal structures, or a planar structure. 

Photoelectron spectra have confirmed the expected trends in the frontier orbitals.The tetrafiuoro derivative 12.12 (R = F) is prepared by treatment of C6F5SNSNSiMc3 with CsF in acetonitrile (Scheme 12.2). Several difiuoro- and trifiuoro-benzodithiadiazines have also been prepared by these methods.In contrast to 12.12 (R = H), which has an essentially planar structure in the solid state,the dithiadiazine ring in the tetrafiuoro derivative is somewhat twisted. In the gas phase, on the other hand, electron diffraction studies show that 12.12 (R = F) is planar whereas 12.12 (R = H) is non-planar. ... 

The seven-membered CN3S3 ring, another ten 7r-electron system, was first obtained as the ester 12.19 (R = COaMe), which is a minor product of the reaction of S4N4 with dimethylacetylene dicarboxylate. It has a planar structure with bond lengths that indicate delocalization. The parent 1,3,5,2,4,6-trithiatriazepine 12.19 (R = H) is obtained as a colourless solid by carefully heating the ester with aqueous HCl followed by decarboxylation. ... 

Intramolecular heteroatom coordination may also influence the stabilities or structures of catenated tellurium compounds. For example, a rare example of a tritelluride, bis[2-(2-pyridyl)phenyl]tritelluride, is stabilized by a Te N contact of 2.55 The ditelluride (2-MeOCelFtCOTe) has an unusual planar structure. Although the C=0 Te interaction is longer (3.11 A) than the Me 0 contact (2.76 A), ab initio molecular orbital calculations indicate that the planarity results predominantly from the former intramolecular connection. 

One important structural feature on which to focus is whether the nitrogen atom lies in the same plane as the three carbon atoms. Electron diffraction experiments have found the ground state to be slightly non-planar. You can determine the planarity of the structures you compute by examining the sum of the three C-N-C angles (for a planar molecule, the sum will be 360°) and by looking at the values of the C2-N-C4-O and C3-N-C4 Hg dihedral angles (in a planar structure, both will be 0°). 

All three optimizations result in very similar planar structures. The bond lengths are all in fairly good agreement with experiment with the exception of the O-H distance. The bond angle predictions are more erratic some are reasonable while others have errors of several degrees. The dihedral angles are both predicted to be essentially zero in all three cases, consistent with a planar structure. 

First, we perform an optimization of the transition structure for the reaction, yielding the planar structure at the left. A frequency calculation on the optimized structure confirms that it is a first-order saddle point and hence a transition structure, having a zero-point corrected energy of -113.67941 hartrees. The frequency calculation also prepares for the IRC computation to follow. 

Unlike formaldehyde, acrolein retains its planar structure in the first excited state. Moving to the first excited state principally affects the C-C-H bond angle, decreasing it almost 5°, and the C-C-C bond angle, increasing it about the same amount. The C-O bond also stretches slightly. 

Figure 4.10 Schematic representation of the (non-planar) structure of some typical crown ethers.

Figure 13.28 Planar structure of (a) [PhSb Mn(CO)2(>j -C5H5)2 ], and (b) [PhAs Cr(CO)5 2]. Note the relatively short Sb-Mn and As-Cr bonds.

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. ... 

Among the possible CC bond conformers for 2,2 -dichlorobiphenyl (DCBP) are syn and anti planar structures and two twist structures. 

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