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CHEM 245- Unit 2

QuestionAnswer
all reactions of benzene are substitution reactions (to keep aromatic ring structure)
electron donating groups bond at 50% ortho, 50% meta
electron withdrawing groups bond at 81% meta
rules for determining aromaticity cyclic, p-orbital, every p-orbital must overlap, pi cloud must contain an odd pair of electrons (4n+2 total electrons)
2 most important aromaticity rules cyclic, 4n+2 total electrons
when do molecules become non-superimposable mirror images? >2 substitutions
clockwise stereochemistry R
counterclockwise stereochemistry S
chiral not identical to its mirror images
achiral has an internal plane of symmetry
clockwise (optically) dextrorotatory (+)
counterclockwise (optically) levorotatory (-)
diastereomer non-superimposable, non-mirror images
do diastereomers have the same physical properties? no
do enantiomers have the same physical properties? yes
# of stereoisomers 2^(chirality centers)
meso compounds mirror image, rotate 180 is the same as original *have chirality centers, but achiral because of the mirror plane
organohalide elimination trend more stable with tertiary compounds
rate law SN2 reactions k[Nu][R3C-X]
SN2 reactions occur in a single step without an intermediate
SN2 rates fastest with fewest substitutions; less electronegative anions=better
SN2 leaving groups gases are best; stable anions of strong acids 2nd
what does SN2 stand for? substitution nucleophilic bimolecular
what does SN1 stand for? substitution nucleophilic unimolecular
rate law SN1 reactions k[starting material]
SN1 only occurs under ____ conditions neutral or acidic
RDS SN1 carbocation formation
are SN1 stereoselective? nope
SN1 leaving groups similar to SN2; less electronegative anions; H2O neutral, OH acidic
rate law E2 k[reactant][base]
E2 requires an antiperiplanar relationship between a H and LG
acyclic E2 more highly substituted alkene is formed (same as cyclic if available)
E1 rate law k[starting material]
if substrates that work well with both E1 and SN1 are combined... a mixture of SN1 and E1 products will form
primary alkyl halides will use what mechanism(s)? SN2 if good nucleophile present E2 if no good nucleophile (base like (CH3)3O)
secondary alkyl halides will use what mechanism(s)? SN2 if good nucleophile present- weakly basic E2 if no good nucleophile (base like (CH3)3O)
tertiary alkyl halides will use what mechanism(s)? SN1 or E1 under acidic or neutral E2 if basic
SN2 needs an available ___ to occur sigma *
SN1 won't occur if _____ is happening on the molecule ring strain
E2 likes what base? t-butoxide
E1 makes a double bond
Created by: melaniebeale