Molecular structure stereoisomer, trans

L. E., Challiner, J.R, and Haws, E.J., Photoq cHzation of N-(diaLkylaminoalkyl) aromatic 1,2-dicar-boximides. X-ray molecular structure of a stereoisomer of 4-benzyl-2-hydroxy-3-phenyl-4,6-diaz-atricyclo[6.4.0.0 > ]dodeca-l(12),8,10-trien-7-one,/. Chem. Soc., Perkin Trans. 1, 121, 1985 (c) Coyle, J.D. and Newport, G.L., Fused imidazoHdines, hexahydropyrazines and hexahydro-1,4-diazepines. Synthesis, 381,1979. 

The two isomers of but-2-ene are stereoisomers because they have exactly the same constitution but a different spatial arrangement of their atoms in space. As we learned in Section 11, a double bond between C atoms consists of the overlap of hybrid orbitals to form a a bond and the sideways overlap of p orbitals to form a tt bond. Because of the ir bond, rotation about a double bond is severely restricted. Molecule (a) cannot be converted into molecule (b) simply by twisting one end of the molecule through 180°, so the two molecules are distinctly different above. To differentiate these two molecules, we call molecule (a) ds-but-2-ene and we call molecule (b) trans-but-2-ene. Because of differences in their molecular structures, the compoimds have different physical properties. For example, the melting points are —139 °C for ds-but-2-ene and —106 °C for tr ns-but-2-ene the boiling points are 3.7 °C for cis-but-2-ene and 0.9 °C for trans-but-2-ene. 

Structural drawings (molecular models too) can be deceiving For example the chlonne atoms in 1 2 dichlorocyclohexane seem much closer to each other in a drawing of the trans stereoisomer than in the cis Make a molecular model of each and measure the distance between the chlorines What do you find" ... 

Two stereoisomers of 1 bromo 4 methylcyclohexane are formed when trans 4 methyl cyclohexanol reacts with hydrogen bromide Write structural formulas or make molecular mod els of... 

How many alkenes have the molecular formula C5H10 Write their structures and give their lUPAC names. Specify the configuration of stereoisomers as cis or trans as appropriate. 

One of a number of molecular entities having the same atomic composition, but different line formulas and/or different stereochemical configurations. A distinction is usually made between structural isomers (molecular entities have the same atomic composition albeit different line formuls), stereoisomers (entities having different arrangements, usually noninterconvertable and nonsu-perimposable, in space), and cis-trans isomers (having different positions for substituents with respect to double bonds or sides of a ring structure). 

Stereoisomerism refers to molecular species that have the same composition and bond sequence but a different arrangement in space of their atoms. Stereoisomers that are characterized by different interatomic distances between certain atoms that are not bound directly are called diastereoisomers. Examples of diastereoisomers are cis-trans isomers of compounds containing C = C bonds and syn-anti isomers of compounds containing C = N bonds. Other diastereoisomers are not based on the presence of a double bond. For example, a molecule with more than one tetrahedral carbon that has different substituents may form diastereoisomers. For example, for a head-to-tail polymerized monosubstituted vinyl monomer, there are three possible structures indicated as isotactic, syndiotactic and atactic, which are schematically shown below ... 

Chemical compounds that have the same molecular formula but different structural formulas are said to be isomers of each other. These constitutional isomers (or structural isomers) differ in their bonding sequence, i.e. their atoms are connected to each other in different ways. Stereoisomers have the same bonding sequence, but they differ in the orientation of their atoms in space. Stereoisomerism can be further divided into optical isomerism (enantiomerism) and geometrical isomerism (cis—trans isomerism). The relationships between the different types of isomerism are shown in Figure 4.1. 

As in the case of [6]paracyclophane (la), irradiation of [6](1,4)naph-thalenophane (55a) produced the Dewar type isomer 53a (s. Scheme 13) [40a]. In remarkable contrast, irradiation (X > 370 nm) of anthracenophane 56a did not give the Dewar type isomer 54a (s. Scheme 13) but yielded five stereoisomers of cyciobutane dimers 85 (Structure 13) [67], Four minor dimers have cis-cis junction around the cyciobutane ring, while the major product has ds-trans stereochemistry. This remarkable photochemical behavior of 56a is ascribed to the high double bond character of the bond a in the anthracenophane system, which is predicted by the semi-empirical molecular orbital calculations. 

A description of the molecular stereochemistry is also included in both the structural formula and nomenclature. Each ring junction can exist in either a cis or trans conformation, yielding six centers of asymmetry or chirality (C-5, 8, 9, 10, 13, 14). Hence, 64 stereoisomers are possible for the ring system alone. With the C-17 side-chain forming a seventh site of asymmetry, the theoretical number of stereoisomers increases to 128. However, in practice, the isomeric possibilities are restricted by the overall conformational limitations of the ring system. 

Stereoisomers that have the same molecular formula, but different arrangements of their groups in space are called cisitrans isomers. These isomers are also sometimes called geometric isomers. The groups located on the same side of the molecule are in the cis formation, while the groups located on the opposite sides of the molecule put it into the trans formation. Figure 13.7 shows the cisjtrans structures of dichloroethene. 

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