Intro To Organic Chem Flashcards
Conditions of cis-trans isomerism
- Restricted rotation about a bond
- Diff functional groups attached to same C atom
Which are cis and which are trans isomers
Cis: 2 identical groups on same side of c=c bond
Trans: 2 different groups on same side of
c=c bond
Relate number of c=c bonds and number of cis trans isomers
If number of c=c bonds that meet the conditions of cis trans isomerism in a compound is n, the maximum number of cis trans isomers for the compound is 2 to the power of n
Effect of cistrons isomerism on boilingpoint
Cisisoner has higher melting point
Has slight net dipole moment so has higher polarity
Pd-pd present so more energy is needed to be absorbed to overcome the stronger pd-pd in cis isomers as compared to weaker id-id in trans isomers
Effect of cis trans isomerism on meltingpoint
Cis isomer has lower melting point
Fits intocrystalline lattice poorly so unable to pack closely
Less energy to break the loosely packed lattice structure
Why are cycloalkanes able to exhibit cisterns isomerism
Free rotation about C-C bond is restricted to maintain geomtetry of ring, considered as restricted rotatiom
Why wont a cycloalkene exhibit cis trans isomerism
Its trans isomee will experience ring strain which is highly unstable
Enantiomeres have…
No plane of symmetry
A chiral centre
Non superimposable mirror images
What is a chiral carbon
Sp3 hybridised
Has 4 different atoms or groups attached to it
About the chiral carbon, the cpd is not symmetrical
What does a dashed bond mean
Bonds that go into the page, away from you, behind the plane
What does a wedged bond mean
Bonds that go out from the page, towards you, in front of the plane
What are the possible reasons to a sample being optically inactive
- Has no enantiomeres/chiral centres present
- Has enantiomerism present but a 50:50 mixture of each enantiomere, forms racemix mixture
Relating number of chiral centres and number of steroisomers
A molecule with n chiral centres has a maximum of 2 to the power of n stereoisomers
What are diastereomers
Stereoisomers which are not mirror images of each other even though they are non superimposable
Relating number of chiral centres and number of double bonds
If a molecule has x chiral centres and y double bonds that give rise to cis trans isomerism = maximum number of stereoisomers it can form is 2 to the power of (x+y)
