Organic Flashcards
Conformation Isomers
Differ by rotation about a single sigma bd
Stereoisomers
Differ by spatial 3-D arrangements
Constitutional(or Structural) Isomers
Differ by the positions of atoms
- 2-chlorobutane vs.
3-chlorobutane
Geometric Isomers
Cis-2-butene vs Trans-2-butene
Enantiomers
Nonsuperimposeable, chiral mirror images
- L-lactic acid vs. R-lactic acid
Diastereomers
Stereoisomers that are not mirror images of each other.
Geometric isomers are also diastereomers.
Racemic mixture
A 50-50 mixture of a pair of enantiomers
Racemization
The conversion of one pure enantiomer to a racemic mixture
Meso compound
A meso compound is one that has chiral centers, but over all the molecule is not chiral.
They posses an internal mirror plane through the center of the molecule.
The mirror images of the molecule is superimposable.
Heterolytic cleavage
Cleavage of a covalent bond where 2 bonding electrons are taken by one atom.
This results in the formation of a cation and an anion
Homolytic cleavage
The cleavage of a covalent bond where one bonding electron is taken by each atom
Br-Br -> Br• + Br•
Rank carbocation stability
3>2>1>methyl
Rank carbocation reactivity
Methyl>1>2>3
It’s opposite of the carbocation stability!
Sn1 mechanism
Rate = k[RX]
Unimolecular reaction
Results in a trigonal planar carbocation which can be attacked from both sides by a nucleophile, which results in a racemic mixture (50% R, 50%S)
Identify enantiomers
Rank substituents according to mass
If 1 to 2 to 3 rotates to the right (or CW) it is R
If 1 to 2 to 3 rotates to the left (or CCW) it is S
Optical rotation
If the plane polarized light is rotated to the left by the chiral center, the molecule is assigned “l” or “negative degrees of rotation”
If plane polarized light rotates to the right it is assigned “d” or “positive degrees of rotation”
Note: R and S enantiomers rotate ppl in equal magnitudes, however the rotation is in opposite directions
Does a racemic mixture rotate plane polarized light?
No. It is optically inactive.
E2 mechanism
Rate = k[base][substraight]
Rxn proceeds through 1 step. There is no carbocation intermediate.
Elimination rxns: Define Saytzeff and Hoffman products
Saytzeff: the eliminated beta H+ comes from the more substituted beta C (generally the major product)
Hofmann: the eliminated beta H+ comes from the less substituted beta C
When will the Hofmann product dominate an elimination rxn?
The less substituted alkene will dominate the rxn as a result of steric hinderance due to:
1: the size of the attacking base
2: the size of the group surrounding the LG
CH3Cl + (n-C4H9)3SnH ->
CH4 + (n-C4H9)3SnCl
CH3MgBr + H2O ->
CH4 + Mg(OH)Br
Areomatic if:
Pi e- = 4n + 2
Huckel numbers!
- 2, 6, 10, 14….
Antiareomatic if:
Pi e- = 4n
