1. A solution has 80% (R)-2-bromobutane and 20% (S)-2-bromobutane a. What is the “enantiomeric excess” of (R)-2-bromobutane? b. If pure (R)-2-bromobutane rotates light 100º to the right, how much rotation would occur for a solution with 80% (R)-2-bromobutane and 20% (S)-2-bromobutane c. If a solution has a 50/50 mixture of (R)- and (S)-2-bromobutane, what would be the enantiomeric excess and the optical purity?
Reactive Intermediates
In chemistry, reactive intermediates are termed as short-lived, highly reactive atoms with high energy. They rapidly transform into stable particles during a chemical reaction. In specific cases, by means of matrix isolation and at low-temperature reactive intermediates can be isolated.
Hydride Shift
A hydride shift is a rearrangement of a hydrogen atom in a carbocation that occurs to make the molecule more stable. In organic chemistry, rearrangement of the carbocation is very easily seen. This rearrangement can be because of the movement of a carbocation to attain stability in the compound. Such structural reorganization movement is called a shift within molecules. After the shifting of carbocation over the different carbon then they form structural isomers of the previous existing molecule.
Vinylic Carbocation
A carbocation where the positive charge is on the alkene carbon is known as the vinyl carbocation or vinyl cation. The empirical formula for vinyl cation is C2H3+. In the vinyl carbocation, the positive charge is on the carbon atom with the double bond therefore it is sp hybridized. It is known to be a part of various reactions, for example, electrophilic addition of alkynes and solvolysis as well. It plays the role of a reactive intermediate in these reactions.
Cycloheptatrienyl Cation
It is an aromatic carbocation having a general formula, [C7 H7]+. It is also known as the aromatic tropylium ion. Its name is derived from the molecule tropine, which is a seven membered carbon atom ring. Cycloheptatriene or tropylidene was first synthesized from tropine.
Stability of Vinyl Carbocation
Carbocations are positively charged carbon atoms. It is also known as a carbonium ion.
1. A solution has 80% (R)-2-bromobutane and 20% (S)-2-bromobutane
a. What is the “enantiomeric excess” of (R)-2-bromobutane?
b. If pure (R)-2-bromobutane rotates light 100º to the right, how much rotation would occur for a
solution with 80% (R)-2-bromobutane and 20% (S)-2-bromobutane
c. If a solution has a 50/50 mixture of (R)- and (S)-2-bromobutane, what would be the enantiomeric
excess and the optical purity?
2. A mixture of two enantiomers has as observed rotation of -18°. The specific rotation of the (-)
enantiomers is -27°. Find the % of the two enantiomers in the solution.
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