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Cyclobutane puckered

The RHF calculation on the thymine dimer in the previous section showed that the ring fusion at the C5 and C6 atoms of two thymine bases created the four-member cyclobutane puckered ring. The same feature is observed with the CAS(3e+4o) level. The puckering leads to axial or equatorial directions for the substituent atoms on the cyclobutane ring the substituent atoms on the two thymine bases differ in their directionality. Especially noteworthy is the direction of the H6A atom. In the neutral T<>T, the H6A atom is equatorial relative to the four-member ring and axial relative to the 7C conjugation system... [Pg.226]

Cyclobutane has less angle strain than cyclopropane and can reduce the torsional strain that goes with a planar geometry by adopting the nonplanar puckered confer matron shown m Figure 3 11... [Pg.115]

Figure 6.42 (a) Cyclobutane, its ring-puckering vibration and dihedral angle, (b) Cyclopentene... [Pg.191]

C4H8 (cyclobutane) ring-puckering, 191 CgHg (benzene)... [Pg.437]

Cyclobutane adopts a puckered conformation in which substituents then occupy axial-like or equatorial-like positions. 1,3-Disubstituted cyclobutanes show small energy preferences for the cis isomer since this places both substituents in equatorial-like positions. The energy differences and the barrier to inversion are both smaller than in cyclohexane. [Pg.147]

FIGURE 3.11 Nonpl anar ("puckered") conformation of cyclobutane. The nonplanar conformation avoids the eclipsing of bonds on adjacent carbons that characterizes the planar conformation. [Pg.115]

Identify the lowest-energy conformer from among those provided cyclopropane, planar and puckered cyclobutane, planar and puckered cyclopentane and chair, half-chair, boat and twist-boat cyclohexane. (If... [Pg.77]

Cyclopropane (115 kj/mol strain) and cyclobutane (110.4 kj/mol strain) have both angle strain and torsional strain. Cyclopentane is free of angle strain but has a substantial torsional strain due to its large number of eclipsing interactions. Both cyclobutane and cyclopentane pucker slightly away from planarity to relieve torsional strain. [Pg.131]

The case of cyclobutane radical cation presents another interesting structural problem. The parent has a puckered ring with symmetry ET from one of its e orbitals leads to a IT unstable radical cation, which distorts to strucmres of Dy ... [Pg.223]

Problem 9.10 Depict the flexible puckered conformation of cyclobutane in a Newman projection. [Pg.172]

The C H bonds in cyclobutanes are relatively normal, but it has been found that the methylene groups are tilted inward,22 whereas one might have expected cross-ring steric interactions to lead to an outward puckering. Bartell and Andersen have explained this as resulting from the bent bonds in cyclobutane.23 In order to retain approximate Clv symmetry at the methylene groups, the bent C-C-C bonds lead to the inward tilt (Figure 5). [Pg.5]

Both silacyclobutane and 1,1-dichlorosilacyclobutane have been shown by electron diffraction to be puckered to about the same extent as cyclobutane. The dihedral angle a is about 30 5°, and is much more than the 14° in l,l,3,3-tetrachIoro-l,3-disiIacycIobutane... [Pg.590]

Weakly semibndging carbonyls, such as those in Os CO), are nearly linear but show some distortion toward the second metal. Of course it is not always dear whether departures from linearity arise from interaction with the metal or because of packing forces in the crystalline solid. All CO ligands are fully nonbridging in the puckered Os4(CO) fi, described as a metal carbonyl analogue of cyclobutane.15 The dark red crystals of Os4(CO)]3 possess nearly planar Os4 units with only terminal CO ligands. [Pg.330]

Did = E, 3C2,2ffrf,2S4. Allene has this symmetry, as do puckered cyclobutane and cyclooctatetraene. [Pg.6]

Although cyclobutane is a puckered molecule (by about 25°), its oxygen analog oxetane is virtually flat. Give a rationale for this behavior. [Pg.180]

Two further halogenated cyclobutanes have in recent years been studied by electron diffraction. Invariably, the rings are found to be non planar. In octafluoro-cyclobutane246 a was found to be 17.4° in one study and 24 3° in another one247). In 1,1-dichlorohexafluorocyclobutane247- the puckering angle is 23.2 2.5 °. [Pg.143]

Molecules with fused carbon-ring systems are considerably less puckered than cyclobutane itself. [Pg.143]

Unlike cyclobutane and its derivatives, many of the four-membered heterocycles usually have planar structures. However, diazetidines are slightly nonplanar or puckered. Earlier, Ruben and co-workers <1974AXB1631> and Loeppky et al. <1991JA2308> have reported X-ray crystallography of a few 1,2-diazetidines. Beckert and co-workers <2002H(57)1257>, while carrying out cyclization of amidrazone with bis-imidoyl chloride, isolated a new crystalline compound which was not the expected triazine but A2-l,2-diazetine or 1/7,4/7-diazetine derivative 22 as established by X-ray analysis. [Pg.629]

Therefore, there are two different values of the N-H bond distance, N-N-H bond angles, C-N-N-H dihedral angles, etc., for the air-isomer. For both the conformers, the four-membered rings are puckered, as in cyclobutane. However, the air-isomer has C symmetry, whereas the /ra .r-isorncr has C2 symmetry. [Pg.648]

In the anti head-to-head dimer of thiocoumarin 70, the cyclobutane ring is puckered and the thiopyran rings adopt conformations between half-chair and twist-boat. Bond lengths and angles have been reported <1994AXC1922, 1995HCA1079>. [Pg.741]


See other pages where Cyclobutane puckered is mentioned: [Pg.726]    [Pg.78]    [Pg.166]    [Pg.726]    [Pg.78]    [Pg.166]    [Pg.191]    [Pg.191]    [Pg.191]    [Pg.192]    [Pg.14]    [Pg.182]    [Pg.474]    [Pg.475]    [Pg.63]    [Pg.147]    [Pg.98]    [Pg.101]    [Pg.350]    [Pg.352]    [Pg.365]    [Pg.171]    [Pg.5]    [Pg.6]    [Pg.263]    [Pg.365]    [Pg.997]    [Pg.142]    [Pg.272]    [Pg.128]    [Pg.518]   
See also in sourсe #XX -- [ Pg.101 ]




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Cyclobutanation

Cyclobutane

Cyclobutane , ring-puckering

Cyclobutanes

Puckered

Puckered, conformation of cyclobutane

Puckering

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