Chem 210 Exam 3 Questions and Correct Answers, With Complete Solution.
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Course
Chem 210
Institution
Chem 210
Chem 210 Exam 3 Questions and Correct Answers, With Complete Solution.
what face of the pi bond can EAR occur from?
either face
how many products do EARs on an alkene form?
4 stereoisomeric products
Brainpower
Read More
in a substitution rxn, what does H-O act as?
nucleophile and replaces...
Chem 210 Exam 3 Questions and Correct Answers,
With Complete Solution.
what face of the pi bond can EAR occur from?
either face
how many products do EARs on an alkene form?
4 stereoisomeric products
Brainpower
Read More
in a substitution rxn, what does H-O act as?
nucleophile and replaces LG
in an elimination rxn, what does H-O acts as?
base and abstracts BH atom
what is a requirement for elimination rxns?
beta hydrogen
what is a requirement for substitution rxns?
leaving group
what is a nucleophile?
electron pair donor- compound using its e- pair to attack another compound
what is an electrophile?
electron pair acceptor - compound being attacked
nucleophiles can become compounds with:
non bonding e- pairs and pi bonds
electrophiles can be compounds with:
open shell atoms and atoms with partial positive charges
substitution rxn:
exchanges one sigma bond for another
elimination rxn:
breaks two sigma bonds to make a pi bond
TS of Sn2 rxn:
sigma bond breaking and sigma bond forming occur simultaneously
how do Sn2 rxns effect configuration
inversion
Sn1 rxn:
multi step: carbocation intermediate, nucleophile attacks C+ (sp2 w empty p orbital)
from either side
E2 rxn:
BH atom and LG prefer to be anti staggered (Newman projection)
tBUO-
strong base, weak nucleophile
, more stable chair conformation:
LG equatorial, BH anti
E1 rxn:
BH atom and LG do not need to be anti, rxn proceeds via C+. LG leaves to form C+,
base attacks BH to form new pi bond
what rxns proceed via the same C+?
Sn1 and E1, products will always be formed together as racemic mixtures!
what is steric hindrance?
the prevention of a reaction at a particular location in a molecule by substituent groups
around the reactive site.
primary C+
no SN1 or E1, but SN2
secondary C+
SN2/E2
tertiary C+
no SN2, SN1/E1 preferred
what is the strength of a nucleophile based on?
charge & polarizability
what does nucleophilicity increase with?
decreased electronegativity and when going down a group
what is a good base?
1. strong bases with pka of CA > 30
2. sterically hindered bases with pka CA > 10
DBU:
predictive model- reagent is nucleophile only
pkaCA<15 (Cl-, Br-, I-, CN-, RS-) & uncharged sp3 hybridized atoms with lone pairs
predictive model- reagent is base only
pkaCA>30 (H-, H3C-, H2N-) & sterically hindered bases w pkaCA>10
predictive model- reagent is strong nuc and strong base
ex: (HO-, H3CO-, H3C-H2C-O-)
predictive model- reagent is weak nuc and weak base
SN2 and E2 rxns dont occur (ex: H2O, R-OH)
SN2 rxn rate
kelectrophilenucleophile
E2 rxn rate
kelectrophilebase
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