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Cyclopropane bent orbitals

The C—C bonds of cyclopropane are bent => orbital overlap is less... [Pg.153]

This increased stability has been explained between the bent orbitals of cyclopropyl rings and the vacant p orbital of the cation carbon. The vacant p orbital lies parallel to C2-C3 bond of the cyclopropane ring and not perpendicular to it. Thus the geometry becomes similar to that of a cyclopropane ring conjugated with an oblefinic bond. [Pg.7]

FIGURE 3.16 "Bent bonds" in cyclopropane. The orbitals involved in carbon-carbon bond formation overlap in a region that is displaced from the internuclear axis. Orbital overlap is less effective than in a normal carbon-carbon ct bond, and the carbon-carbon bond is weaker. [Pg.106]

Angle strain exists in a cyclopropane ring because the orbitals comprising the carbon-carbon cr bonds cannot overlap as effectively (Fig. 4.9a) as they do in alkanes (where perfect end-on overlap is possible). The carbon—carbon bonds of cyclopropane are often described as being bent. Orbital overlap is less effective. (The orbitals used for these bonds are not purely sp they contain more p character.) The carbon-carbon bonds of cyclopropane are weaker, and as a result the molecule has greater potential energy. [Pg.167]

Strong sp -sp a bonds are not possible for cyclopropane, because the 60° bond angles of the ring do not permit the orbitals to be properly aligned for effective overlap (Figure 3.10). The less effective overlap that does occur leads to what chemists refer to as bent bonds. The electron density in the carbon-carbon bonds of cyclopropane does not lie along the internuclear- axis but is distr-ibuted along an arc between the two carbon atoms. The r-ing bonds of cyclopropane are weaker than other carbon-carbon a bonds. [Pg.114]

The noteworthy point is a shortening of C-C bond distance as compared to the aliphatic C-C bond distance which is 1.54 A. This shortening manifests itself in the development of special character of the bonds. Since the sp orbitals of carbon now cannot overlap as effectively as they do in alkanes where perfect end-on overlap occurs the bonds in cyclopropane becomes bent and weak and also lead to an angle strain and so the molecule has greater potential energy. So this bent or banana bond accounts for the most of the ring strain. [Pg.173]

An important example of a 1,2-C migration (C—C insertion) is the ring expansion of chlorocyclopropylcarbene (54) to 1-chlorocyclobutene (Scheme 7.20). The 1,2-C shift takes precedence over 1,2-H shift. Chloromethylenecyclopropane (55), the putative product of a 1,2-H shift, is not formed. Interaction of the electron-rich bent cyclopropane C—C bond(s) with the vacant p orbital of carbene 54 leads to a more favorable rearrangement pathway than the alternative Oc-H/p interaction leading to 55. [Pg.305]

The structures of bicyclic and polycyclic small-ring compounds have attracted some interest. The relationship between the C-C-H bond angles at the bridgehead of bicyclo[1.1.0]butane (2) and the angle between its cyclopropane rings has been studied.31 Bicyclobutane and most other cyclopropane derivatives have bonds that are formed from orbitals that are bent in the same direction. However, with some mm -fused bicyclic compounds containing a cyclopropane... [Pg.6]

FIGURE 7. Forster-Coulson-Moffltt bent bond orbitals of cyclopropane. Reprinted from E. Honegger, E. Heilbronner and A. Schmelzer, Nouv. J. Chim., 6,519 (1982) by permission of Gauthier-Villars Publishers... [Pg.56]

The conceptual interrelations of species with three-membered rings and those with double bonds are among the oldest and best-established in the study of strained species18,21. These interrelations have ramifications in the understanding of reactivity and stability patterns, spectra, geometry and electronic delocalization and have been expressed in terms of the Walsh (Walsh Sugden), a and n orbitals, bent and banana bonds, and cyclopropane and cycloethane 22. For this chapter we will but consider some of the thermochemical aspects. [Pg.227]

The direct observation of ion 46 is of particular interest in that it clearly does not involve a significantly opened cyclopropane ring, which could lead to the formation of an allylic cation. Thus, it must be considered as a bent cyclopropyl cation.164-170 It is, however, clear that the Ci-C6 ct-bond must to some degree interact with the empty p orbital at Cn and that homoconjugation between them becomes the important factor in stabilizing such a bent cyclopropyl species. [Pg.116]

Angle strain in cyclopropane. The bond angles are compressed to 60° from the usual 109.5° bond angle of sp3 hybridized carbon atoms. This severe angle strain leads to nonlinear overlap of the sp3 orbitals and bent bonds. ... [Pg.111]

Spiroacylal 2 was designed under the rationale that the constraint of the carbonyl groups into a conformation in which overlap of their 7r-orbitals with the bent bonds of the cyclopropane is assured should dramatically increase the vulnerability of the cyclopropane toward nucleophilic attack.8 Experimental support for this notion is abundant.8 Spiroacylal 2 is considerably more reactive than 1,1-dicarbethoxycyclopropane in such reactions. For instance, reaction of 2 with piperidine occurs at room temperature. The corresponding reaction in the case of the diester is conducted at 110°C.5 Reactions with enolates also occur under mild conditions.8 Compound 2 reacts with the weak nucleophile pyridine at room temperature to give a betaine.8 An illustrative mechanism for the reaction of the acylal 2 with aniline to afford 2-oxo-l-phenyl-3-pyrrolidinecarboxylic acid (3) is... [Pg.36]


See other pages where Cyclopropane bent orbitals is mentioned: [Pg.223]    [Pg.169]    [Pg.66]    [Pg.54]    [Pg.114]    [Pg.6]    [Pg.115]    [Pg.181]    [Pg.182]    [Pg.268]    [Pg.65]    [Pg.193]    [Pg.92]    [Pg.724]    [Pg.170]    [Pg.1]    [Pg.1]    [Pg.5]    [Pg.13]    [Pg.152]    [Pg.121]    [Pg.144]    [Pg.169]    [Pg.195]    [Pg.23]    [Pg.169]    [Pg.176]    [Pg.42]    [Pg.111]    [Pg.166]   
See also in sourсe #XX -- [ Pg.187 ]




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