Trans/anti conformation

The molecular conformation of trans- [(tBu)2PPh]2Ir(CO)Cl has been investigated by 31P 1H NMR spectroscopy and reveals four diastereoisomers two major conformations in which the phenyl groups are mutually anti and orientated on the same side or opposite sides of the coordination plane, and two minor isomers in which the two phenyl groups are syn to the CO ligand.557... 

In trans-2,3-di-F- and rrans-2,3-di-Cl-l,4-dioxane, as in the OR analogs, the halogens adopt the diaxial conformation [79NJC145, 79JOC2274 84SPL307]. The corresponding cis isomers, c/s-rrans-2,3,5,6-tetrachloro-, trans-anti-trans-2,3,5,6-tetTachloTO-, 2,2,3,3-tetrachloro-, and 2,2-dichloro-... 

A slightly more complicated case than ethane is that of a 1,2-disubstituted ethane (YCH2—CH2Y or YCHj—CH2X),197 such as n-butane, for which there are four extremes a fully staggered conformation, called anti, trans, or antiperiplanar another staggered con-... 

Gauc/ie-H202 has C2 symmetry. What are the symmetries of the eclipsed (ds) conformation and the anti (trans) conformation ... 

A more striking example of the influence of conformation on the reaction outcome is seen in the nitrous acid deamination of 2-aminocyclohexanols which takes place by rearrangement of a group on the carbinol carbon that is anti to the developing carbocation. The deamination reaction is very fast and the products reflect the population of the chair conformers. The trans isomer exists mainly in the diequatorial conformer thus the only group anti to the amino... 

Stereochemistry No preferred conformation Anti-periplanar elimination (trans-diaxial in cyclohexanes)... 

The stereochemical outcome of the reaction (inversion of the configuration at the oxirane carbon) was explained by the approach of Cp2ZrHCl from the less hindered side of the stable gauche conformer of the vinyloxirane (Scheme 19). Cis-epoxides gave only syn-trans cyclopropyl carbinols, whereas trans-oxiranes gave mixtures of anti-trans and anti-cis isomers. 

The presence of about 10% boat-chair conformation in trans-syn-trans 1,2,5,6-tetrabromocyclooctane (XI) (see Section VII. C) has been confirmed by 251 MHz IH nmr. 7 5) The trans-anti-trans isomer of this compound has been found by 251 MHz IH nmr to be an approximately 1 1 mixture of a crown-family and a boat-chair conformation. 5)... 

Six-membered acetal rings fused to seven-membered rings are found in acetals formed directly from mannitol and certain of its derivatives. The 1,3 2,5 4,6-structure has been proved for the tri-O-methylene " and tri-0-ethylidene " derivatives of mannitol, and the 1,3 2,5-structure for the di-O-methylene derivative of 6-deoxy-L-mannitol. " These acetals are markedly more stable than the 2,4 3,5-diacetals discussed above. Their stability has been related to the probable mechanism of formation,"" but is also understandable on conformational grounds. " The ring junctions are trans, and the triacetals LXI have the trans-anti-trans configuration, which... 

In summary, the stereochemical course of cation-7t cyclizations is determined by stereoelectronic and conformational effects. Concerted cation-Ti cyclizations usually involve a stereospecific trans-addition (axial attack) of the carbocation to the double bond. This is exemplified by Johnson s biomimetic synthesis ( )-progesterone, which possesses a trans, anti, trans-fused ring system." - ... 

The main remark is that the linear, hydrogen bond free, s-Trans-Anti-Trans (TAT) is the most stable conformations of glyoxalmonoxime, both at B3LYP/ 6-31G and MP2/6-31G level of calculations [188]. The strength of the... 

It is accepted that triterpenoids in plants are formed through an all tram-anti conformation of squalene while lanosterol is formed through a tram-syn-tram-anti-trans-anti conformation to give the protosteroid cation (Fig. 19). 

Figure 1.2.2 The description of conformers of an A- X-Y-B system. First row definition of torsion angle ((). Second row definition of left- and right-handed as well as of syn(cis) and anti (trans). Third row definition of defined conformers, always relating to the relative position of A and B.

In its most stable conformation, the trans stereoisomer has no (3 hydrogens anti to Br all four are gauche. Strain increases significantly in going to the E2 transition state, and the rate of elimination is slower than for the cis stereoisomer. 

Mo(=CHR )(N-2,6-/-Pr2-CsH3)(OR )2 (38e) and (380 High trans conformation anti 7-methylnorbornene (e) is much more reactive than its syn isomer [457]... 

The reaction of bromine with cyclohexene involves anti addition, which generates, initially, the diaxial conformation of the addition product that thai imdergoes a ring flip to the diequatorial conformation of trans-1,2-dibromocyclohexane. 

---