Trans Isomerism in Alkenes

Change the following old names to new, post-1993 names, and draw the structure of each compound  

Broken w bond after rotation (p orbitals are perpendicular) 

The lack of rotation around carbon-carbon double bonds is of more than just theoretical interest it also has chemical consequences. Imagine the situation for 

These two compounds are identical they are not cis-4rans isomers. 

These two compounds are not identical they are cis-trans isomers. 

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Figure 6.4 The requirement for cis-trans isomerism in alkenes. Compounds that have one of their carbons bonded to two identical groups can t exist as cis-trans isomers. Only when both carbons are bonded to two different groups are cis-trans isomers possible.

Cis-trans isomerism in alkenes arises because the electronic structure of the carbon-carbon double bond makes bond rotation energetically unfavorable at normal temperatures. Were it to occur, rotation would break the pi part of the double bond by disrupting the sideways overlap of two parallel p orbitals (Figure 23.2). In fact, an energy input of 240 kj/mol is needed to cause bond rotation. 

Another approach for a stereochemical index Q encoding information on cis-trans isomerism in alkenes was described by Estrada on including a corrected electron charge density calculated with the MOP AC version 6.0, the following... 

Cis—trans isomerism in alkenes is possible only when both of the double-bond carbon atoms have two different groups. 

Thus far, we have considered cis-trans isomerism in alkenes containing only one carbon-carbon double bond. For an alkene with one carbon-carbon double bond that can show cis-trans isomerism, two cis-trans isomers are possible. For an alkene with n carbon-carbon double bonds, each of which can show m-fraw3 isomerism, 2" ris-frawi isomers are possible. 

Some Facts about Double Bonds The Orbital Model of a Double Bond the Pi Bond Cis Trans Isomerism in Alkenes A WORD ABOUT... 

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