Ch 7 Substitution reactions

Question 1

Leaving Group

Answer 1

a species that capble of separating from the molecule

1. leaving groups withdraw electron density vi induction rendering the adjecent carbon atom electrpholic
2. the leaving group can stablize any negative charge that may develop asthe result of the leaving group separating

Question 2

concerted

Answer 2

simultaneously

Question 3

secound order

Answer 3

the rate is linearly dependent on the concentrations of the two different compounds (Nu:- and E+)

Question 4

biomolecular

Answer 4

the step involes two chemical enities

Question 5

when the alpha postion is a chirality center the configuration ___________.

Answer 5

when the alpha position is a chirality center, a change in configuration is generally observed

Question 6

back side attack

Answer 6

the back side (the side opposite the leaving group) and never from the front side

Question 7

stereospecific

Answer 7

the configuration of the product is dependent on the configuration of the starting material

Question 8

alkyl halide reactivty Sn2

Answer 8

1>2>3

Question 9

SN1 reactions

Answer 9

two step mech

1. the loss of the leaving group to form a carbocation
2. Nu attack on the carbocation intermediate

the ionzation reaction is the rate determining step, the rate equation is first order in the econcentration if the alkyl suvstrate only

produce racemized tetrahedreal stereocenter bearing the nu- b/c the intermediate carbocation is planar sp2 hybridized and the nu- can attack from either side

Question 10

alkyl halide Sn1 reactivity

Answer 10

3>2>1>methyl

Question 11

stereochemistry of Sn1 reactions

Answer 11

sn1 reactions involve formation of an intermedicate carbocation, which can then be attacked from either side,leading to both inversion of congiguration and retention of configuration

Question 12

Sn2 reactions. draw it

Answer 12

one concerted step

Nuc attack + loss of LG

the rate of reaction is first order in both the consentrations of the nucleophile and the concentration of the alkyl substrate

proceed by inversion of configuration at the carbon center

Question 13

Strong Nu:

Answer 13

I^- HS^- HO^- Br^- H₂S RO^-

Cl^- RSH N=-C^-

Question 14

weak Nu^-

Answer 14

F^- H₂O ROH

Question 15

Good leaving groups

Answer 15

good leaving groups are the conjugate base of strong acids

Question 16

substition reactions. Draw it

Answer 16

in these reactions an electron pair on the nucleophile (which is usually negatively charged ) attacks the carbon atom with parttical postive charge that is bound to an electronegative atom.the electron negative atom is diplaced and referred to as a leaving group

Question 17

generalizations on relative strengths of Nu

Answer 17

1. negatively cahred nucleophiles react faster in substitition reactions than neutral nucleophiles
2. nu strength is in the same order as base strength when the nu atoms are in the same period (less electronegative ??)
3. nu strength increases with increasing atomic size when nu atoms are in the same column

Question 18

in a basic hydrolysis reaction a leaving group is replaced by

Answer 18

hydroxide froming a neutral alcohol

Question 19

vinylic halide do not undergo ______ reactions

Answer 19

sn2

Question 20

benzylic and ______ halides undego Sn2 reactions faster then corresponding simple alkyl halides

Answer 20

allylic

Question 21

aryl halides and phenols do not undergo ____ reactions

Answer 21

sn2 or sn1

Question 22

cleavage of an ether usually requires

Answer 22

a strong acid that has a conjugate bas which is a strong nu- such as HBr and HI

Question 23

ring opening reaction of epoxides occur by

Answer 23

sn2 mech whether or not the ring oxygen atom is protonated

the regiochemistry of the nu attack does depend on wether or not the oxygen atom if protonated first

when it is protonated the nu attack the more highly substituted carbon atom ,it inverts the configuration at the reaction site and retains the configuration at the site that becomes the alcohol