CCC bond angle

Which conformation is more stable, anti or gauchel What evidence is there for steric repulsion between methyl groups in the gauche conformation (Hint Look for distortions in the CCC bond angles as a function of conformation.)... 

Cyclopropane, C.H, is a hydrocarbon composed of a three-membered ring of carbon atoms, (a) Determine the hybridization of the carbon atoms, (b) Predict the CCC and HCH bond angles at each carbon atom on the basis of your answer to part (a), (c) What must the real CCC bond angles in cyclopropane be (d) What is the defining characteristic of a cr-bond compared with a ir-bond, for example (e) How do the C—C cr-bonds in cyclopropane extend the definition of conventional o-bonds (f) Draw a picture depicting the molecular orbitals to illustrate your answer. 

The availability of 18 in one synthetic step via direct oxidative functionalization of HCTD [19-21] allows exploration of this valuable compound s chemistry, for the first time. Thus, the reaction sequence shown in Scheme 9 has been utilized to prepare a novel polycyclic alkene, 30, whose s unmetry properties require that its central, tetrasubstituted C=C double bond be completely planar (in the isolated molecule). The constraints imposed by the polycarbocyclic cage framework cause the CCC bond angles about the central C=C double bond in 30 to deviate significantly from the preferred value of 120°, thereby introducing additional steric strain in this molecule beyond that which is associated with its framework alone. 

These discrepancies result (a) from the harmonic approximation used in all calculations [to,- (theory) > v, (exp)], (b) the known deficiencies of minimal and DZ basis sets to describe three-membered rings [polarization functions are needed to describe small CCC bond angles a>,(DZ + P) > w,(DZ) > to,(minimal basis)] and (c) the need of electron correlated wave functions to correctly describe the curvature of the potential energy surface at a minimum energy point [ [Pg.102]

Acrylonitrile, CH2CHCN, is used in the synthesis of acrylic fibers (polyacrylonitriles), such as Orion. Write the Lewis structure of acrylonitrile and describe the hybrid orbitals on each carbon atom. What is the approximate value of the CCC bond angle ... 

The structure of isotactic polystyrene has been studied by means of x-ray diffraction [Natta and Corradini (152,153)]. It is found that the chain configuration is helical, with three monomer units per repeat exactly as in polypropylene. The only difference is that the chain repeat of 6.65 A in polystyrene implies an opening of the CCC bond angles in the chain to 116.5°. The orientation of the benzene ring is apparently not settled. In the above structure, if the axis of the benzene ring were perpendicular to the helix axis, then the plane of the benzene ring would be almost exactly perpendicular to the helix axis. In a variation of this structure proposed on the basis of stereochemical considerations [Bunn and Howells (30)], and shown in Fig. 16, the plane of the benzene ring... 

Figure 15-20. TD/BP86/6-31G energies of excited electronic states for p-MO-DPA (left) and p-CN-DPA (right). The energies are calculated at the optimized CIS/6-31G geometries of A" (p-CN-DPA and p-MO-DPA) electronic states at fixed central CCC bond angles. (Reprinted with permission from Ref. [44].)...

CCC bond angle is larger than 120°. Analysis of the anisotropic components of the carbon-13 hyperfine splitting confirms this and shows that... 

Another useful concept is that certain sizes of ring are more easily formed than others. Let us first consider the formation of a six-membered ring. Draw out a six-carbon aliphatic chain in such a manner that the ends are close together. Remember that in an aliphatic carbon the hybridisation is sp, and so the CCC bond angle is about 109°. 

The HCH bond angles at carbon in methane are I09°28 (in most saturated hydrocarbons, values of ca. 111° arc found for CCC bond angles). 

Interestingly, there is one substrate that is predicted by molecular mechanics calculations to ionize still more slowly than 38. This compound is 39, a derivative of the hydrocarbon known as cubane, and in which the CCC bond angles are 90°. However, in contrast to 36, and especially 38, the ester 39 undergoes SN1 reaction in methanol much faster than expected. The product from 39 is the corresponding methyl ether 40 (see Eaton9). 

PCC and CCC bond angles (126.6 and 127.7°) involving the a- and /S-carbon atoms of the allyl group of (191) are considerably increased compared to sp angles. It has been concluded that the ylide character cannot be estimated from the P—C bond length on the basis of complete ylene structure for methylenetriphenylphosphorane. Studies are also reported for the imino-phosphorane (193), (194), monoclinic triphenylphosphine oxide, the... 

The geometrical model applied for trans-butadiene in this work is the same as the one applied usually in studies on polyene chains [1]. In dynamic simulations the coordinates perpendicular to the chain axis ( y0) of the CH units are usually kept constant, and only the coordinates u, parallel to the axis are varied. In this way for an ideally dimerized chain with the bond alternation uo=0.037 A [1] one obtains 1.336 A for the short CC-bond (r,), 1.465 A for the long CC-bond (r, and 119.9° for the CCC-bond angle [Pg.210]

The standard C—C bond length / is 0.154 nm, the standard CCC bond angle is tetrahedral, 109.5°, and the planar zigzag structure is the most likely conformation. The... 

What is the hybridization of each carbon in CH3CH=CHC=CH What are the CCC bond angles ... 

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