Organic Chemistry I (Test 3)

Front 1

what are alkyl halides?

Back 1

organic molecules containing a halogen atom X bonded to a sp3 hybridized carbon

Front 2

what is the general formula for alkyl halides?

Back 2

CnH2n+1x

Front 3

what is the most important factor in determining the course of an alkyl halide's reaction?

Back 3

whether the alkyl halide is primary, secondary or tertiary.

Front 4

what are vinyl halides?

Back 4

halides that have a halogen bonded to a C=C double bond

Front 5

what are aryl halides?

Back 5

halides that have a halogen atom bonded to a benzene ring.

Front 6

what are allylic halides?

Back 6

halides that have X (halogen) bonded to the carbon ADJACENT to a C=C double bond.

Front 7

what are benzylic halides?

Back 7

halides that have X (halogen) bonded to the carbon ADJACENT to a benzene ring.

Front 8

what is the hybridization of the carbon that the halogen atoms are bonded to in vinyl halides and aryl halides?

Back 8

sp2

Front 9

what is the hybridization of the carbon that the halogen atoms are bonded to in allylic halides and benzylic halides?

Back 9

sp3

Front 10

do vinyl and aryl halides undergo substitution? (SN1 or SN2)

Back 10

NO!

Front 11

do allylic and benzylic halides undergo substitution? (SN1 or SN2)

Back 11

YES

Front 12

alkyl halides are ______ polar molecules

Back 12

weakly

Front 13

what kind of intermolecular forces exist in alkyl halides?

Back 13

dipole dipole interactions because of their polar C-X bond

Front 14

why aren't alkyl halides capable of of intermolecular hydrogen bonding?

Back 14

because apart from the dipole dipole interaction between the C and X, the rest of the molecule contains only C-C and C-H bonds.

Front 15

what is the chemistry of alkyl halides determined by?

Back 15

their polar C-X bond

Front 16

what kind of reactions do alkyl halides undergo with nucleophiles?

Back 16

substitution

Front 17

what kind of reactions do alkyl halides undergo with bases?

Back 17

elimination

Front 18

what are the 3 necessary components in any substitution reaction?

Back 18

1) sp3 hybridized C
2) nucleophile
3) leaving group

Front 19

what effect does the polar C-X bond have on the carbon atom in each Ch3X molecule??

Back 19

makes the carbon atom electron deficient (electrophillic)

Front 20

what atoms can constitute a leaving group?

Back 20

most commonly the halogen atoms

(but OH2+ and N2+ are also encountered occasionally)

Front 21

what constitutes a nucleophile?

Back 21

nucleophiles always contain a lone pair or a pi bond, and sometimes, not always, they contain a negative charge.

Front 22

what are substitution reactions also called?

Back 22

nucleophilic substitution reactions

Front 23

are nucleophiles electron rich or electron deficient?

Back 23

electron rich

Front 24

nucleophilic substitutions are what kind of acid-base reaction?

Back 24

lewis acid-base reactions.

Front 25

in a substitution reaction the ________ donates it's electron pair and the ______ alkyl halide accepts it.

Back 25

nucleophile donates its electron pair, the alkyl halide (lewis acid) accepts it

Front 26

in substitution reactions, what is the lewis acid and what is the lewis base?

Back 26

the lewis acid is the alkyl halide and the lewis base is the nucleophile.

Front 27

what kind of cleavage occurs when the C-X bond is cleaved?

Back 27

heterolytic

Front 28

what kind of charge does the substitution product bear when when a neutral nucleophile is used in the reaction?

Back 28

positive

Front 29

what happens to all of the atoms originally bonded to the nucleophile after substitution occurs?

Back 29

they stay bonded to it!

Front 30

what happens when the substitution product bears a positive charge and also contains a proton bonded to O or N?

Back 30

the initial substitution product loses a proton in a bronsted-lowry acid-base reaction, forming a neutral product.

Front 31

what are the steps in drawing products for any nucleophilic substition?

Back 31

1) identify the sp3 hybridized carbon with the leaving group
2) identify the nucleophile (species with lone pair or pi bond)
3) substitute the nucleophile for the leaving group and assign charges.

Front 32

what makes a good leaving group?

Back 32

all good leaving groups are weak bases with strong conjugate acids having low pka values(the more stable the leaving group is, the better able it is to accept electrons)

Front 33

what trend does the quality of a leaving group follow on the periodic table?

Back 33

quality of leaving group increases across to p table to the right and down the p table! (the bigger the atom, the more stable)

Front 34

what are some good leaving groups?

Back 34

Cl, Br, I, OH2+

Front 35

what are some bad leaving groups?

Back 35

F, OH, NH2, H, R

Front 36

do neutral compounds or charged compounds make better leaving groups?

Back 36

neutral

Front 37

what is the rule about whether or not equilibrium will favor the products of nucleophilic substitution?

Back 37

equilibrium will favor the products of a substitution when the leaving group is a WEAKER base than the nucleophile.

Front 38

what is the difference between bases and nucleophiles?

Back 38

what they attack

Front 39

what do bases attack?

Back 39

protons (hydrogen)

Front 40

what do nucleophiles attack?

Back 40

usually carbons (electron deficient atoms besides hydrogen)

Front 41

what does a conjugate acid have?

Back 41

one more hydrogen

Front 42

what is the trend on the periodic table regarding strength of a nucleophile?

Back 42

across the p table to the left (nucleophilicity increases as basicity increases)

Front 43

what are two rules regarding strength of nucleophiles? (apart from p table position)

Back 43

1)for 2 nucleophiles with the same nucleophilic atom, the stronger base is the stronger nucleophile
2)a negatively charged nucleophile is always stronger than it's conjugate acid

Front 44

the smaller the pka the ___ the acid...

Back 44

the stronger the acid

Front 45

what is basicity?

Back 45

a measure of how readily an atom donates its electron pair to a PROTON (characterized by equilibrium constant ka in an acid-base reaction)

Front 46

what type of property is basicity?

Back 46

thermodynamic

Front 47

what is nucleophilicity?

Back 47

a measure of how readily an atom donates its electron pair to OTHER ATOMS (characterized by the rate constant k, of a nucleophilic substitution)

Front 48

what type of property is nucleophilicity?

Back 48

kinetic

Front 49

what can discredit the rule that a strong nucleophile is also a strong base?

Back 49

nucleophilic size and steric factors

Front 50

what is steric hinderance?

Back 50

a decrease in reactivity resulting from the presence of bulky groups at the site of a reaction.

Front 51

how does steric hinderence effect nucleophilicty and basicity?

Back 51

steric hinderance decreases nucleophilicty but NOT basicity.

Front 52

why aren't bases effected by steric hinderance?

Back 52

because they pull off small, easily accessible hydrogens (protons)

Front 53

why are nucleophiles effected by steric hinderence?

Back 53

because they must attack a crowded tetrahedral carbon, so bulky groups get in the way and decrease reactivity.

Front 54

what do you call sterically hindered bases that are poor nucleophiles?

Back 54

nonnucleophilic bases

Front 55

which substitution reaction features second order kinetics?

Back 55

Sn2 (both the alkyl halide and nucleophile appear in the rate equation)

Front 56

what effect does altering the amount of either the alkyl halide or the nucleophile have on the rate?

Back 56

altering either of the two will effect the rate to an equal extent.

Front 57

what does the energy diagram for Sn2 reactions look like?

Back 57

one step so there is one hump with the products written lower than the starting materials.

Front 58

in an sn2 reaction what are the two possible directions from which the nucleophile can attack?

Back 58

1)frontside (same as leaving group)
2)backside (opposite of leaving group)

Front 59

what sterochemistry occurs as a result of a frontside sn2 reaction?

Back 59

frontside sn2 attack results in retention of configuration around the stereogenic center (nothing changes as X and Nu- swap places)

Front 60

what stereochemistry occurs as a result of attack on the backside in an sn2 rxn?

Back 60

inversion of configuration!

Front 61

what relationship do the products that form from an sn2 reaction have if one is frontside attack and one is backside attack?

Back 61

not the same compound! they are enantiomers! (non imposable mirror images!)

Front 62

what direction of attack occurs in ALL sn2 reactions??

Back 62

backside attack! which results in inversion of configuration at the stereogenic center

Front 63

why do all sn2 reactions occur via backside attack?

Back 63

both the nucleophile and leaving group are electron rich and these charges repel each other. backside attack allows them to stay far away from one another.

Front 64

in the transition state during an sn2 reaction the nucleophile and leaving group are how many degrees away from each other?

Back 64

180

Front 65

what does the hammond postulate relate? and what rxn does it apply to?

Back 65

rate to stability (in sn1 rxn)

Front 66

what does the hammond postulate say? 2 things

Back 66

1) the rate of an sn1 reaction increases as the number of R groups on the carbon with the leaving group increases
2) the stability of a carbocation increases as the number of R groups on the positively charged carbon increases

Front 67

what does the hammond postulate imply overall?

Back 67

the rate of an sn1 reaction increases as the stability of the carbocation increases

Front 68

what does the hammond postulate say regarding TS?

Back 68

the hammond postulate says the TS of a reaction resembles the structure of the species to which it is closer in energy

Front 69

according to the hammond postulate, in exothermic reactions the TS is closer in energy to what?

Back 69

the products

Front 70

according to the hammond postualte, in endothermic reactions the TS is closer in energy to the what?

Back 70

the reactants

Front 71

in sn1 reactions the formation of the carbocation is what in terms of energy?

Back 71

endothermic

Front 72

what does the stability of a carbocation determine?

Back 72

the rate of it's formation

Front 73

in determining between sn1 and sn2, increasing alkyl substitution favors....

Back 73

sn1

Front 74

in determining between sn1 and sn2, decreasing alkyl substitution favors...

Back 74

sn2

Front 75

between sn1 and sn2: what types of reactions do methyl and PRIMARY alkyl halides undergo?

Back 75

sn2 only

Front 76

what types of reactions do TERTIARY halides undergo? (between sn1 or sn2)

Back 76

sn1 only

Front 77

do SECONDARY halides undergo sn1 or sn2 reactions?

Back 77

can undergo both

Front 78

how does the strength of the nucleophile effect the rate of an sn1 reaction?

Back 78

IT DOESN'T!! because it isn't in the rate equation!

Front 79

how does the strength of the nucleophile effect the rate of an sn2 reaction?

Back 79

strong nucleophiles favor sn2 reactions!

Front 80

what effect do weak nucleophiles have on nucleophilic substitution reactions?

Back 80

weak nucleophiles favor sn1 reactions

Front 81

what effect does the quality of the leaving group have on the rate of both sn2 and sn1 reactions?

Back 81

the better the leaving group, the faster the rate of the reaction

Front 82

what is the order of quality of leaving groups from worst to best!?why?

Back 82

F, Cl, Br, I (down the p table!- more readily accepts electrons, WEAKER BASE!

the weaker the base the better the leaving group!!!!!!

Front 83

alkyl halides undergo elimination reactions with what?

Back 83

bronsted lowry bases

Front 84

what is lost and formed in an elimination rxn?

Back 84

the elements of HX are lost and an alkene is formed

(new pi bond in product!)

Front 85

what do you call the removal of elments HX?

Back 85

dehydrohalogenation

Front 86

what occurs during dehydrohalogenation? in E rxn

Back 86

introduction of a pi bond and formation of an alkene

Front 87

what are the steps in drawing the products of any elimination reaction?

Back 87

1) find the alpha carbon (the sp3 hybridized carbon bonded to the leaving group)
2) identify all the beta carbons with H atoms
3) remove the elements of H and X from the alpha and beta carbons and form a pi bond

Front 88

what's the major product of elimination reactions?

Back 88

alkenes

Front 89

what is true about the bonding structure of C=C double bonds?

Back 89

sp2 hybridized, trigonal planar and all bond angles are 120 degrees.

Front 90

what's a monosubstituted alkene?

Back 90

an alkene with one carbon bonded to the double bond

Front 91

what is a disubstituted alkene?

Back 91

an alkene with 2 carbon atoms bonded to the carbon of the double bond.

Front 92

in an elimination reaction, for two stereoisomers to be possible, what must be true regarding the C=C double bond?

Back 92

the 2 groups attached to each carbon must be different from one another

Front 93

which alkenes are more stable, cis or trans? why?

Back 93

trans, because the groups are farther apart-reducing steric strain!

Front 94

elmination: increasing number of R groups has what effect on alkenes? why?

Back 94

increases stability- the more R groups, the more stable...why? because

Front 95

if trans isomers are more stable when the R groups are farthest apart, why do more R groups increase stability of the alkene?

Back 95

because R groups are sp3 hybridized, whereas the carbon atoms of the double bond are sp2 hybridized and the higher the %s character, the more readily an atom accepts electron density... sp2= 33%s and sp3= 25% s... sp3 are more able to donate electron density, sp2 are more able to accept e- density.

Front 96

why are trans alkenes more stable than cis alkenes?

Back 96

trans have fewer steric interactions

Front 97

why does increasing alkyl substitution stabilize an alkene?

Back 97

by an electron-donating inductive effect

Front 98

what is the most common mechanism for dehydrohalogenation ( removal of components off of alpha, beta carbons)?

Back 98

E2

Front 99

what MUST be connected to a beta carbon for an E2 reaction to take place?

Back 99

at least one hydrogen DIRECTLY bonded to a Beta carbon!!!

Front 100

in e2 reactions how does the strength of the base effect the rate equation?

Back 100

e2 reaction rate increases as strength of base increases (analogous to sn2 w/ nucleophile)

Front 101

in E2 reactions, the better the leaving group, the ____ the reaction?

Back 101

the better the leaving group the faster the e2 reaction (like sn2!)

Front 102

a strong base does what to an e2 reaction?

Back 102

increases the reaction rate

Front 103

do sn2 and e2 reactions differ in how the R group effects the reaction rate?

Back 103

YES (exact opposites in this sense)
SN2- methyl and primary are best
E2- tertiary is best!

Front 104

in what ways are sn2 and e2 reactions alike in the way they effect rxn rate? in what ways are they different?

Back 104

alike:
1)identity of base/nucleoohile,
2)the leaving group
3)the solvent.

different:
4)R groups

Front 105

what is zaitsev's rule?

Back 105

(E2) the major product in beta elimination is the product is the more stable product- the one with the most substituted double bond

Front 106

what is the critical difference between E1 and E2 reactions?

Back 106

the TIMING that the bonds are broken and formed

Front 107

in an E1 reaction the leaving group comes off _____ the beta proton (hydrogen) is removed, and the reaction occurs in _____ step(s)

Back 107

before, and two steps

Front 108

in an E2 reaction, the leaving group comes off ____ the beta proton (hydrogen) is removed, and the reaction occurs in _____ step(s)

Back 108

at the same time, and in one step

Front 109

how is the rate of E1 reactions effected by the number of R groups?

Back 109

the rate of E1 reactions increases as the number of R groups on he carbon with the leaving group increases

Front 110

which elimination reaction to strong bases favor?

Back 110

sn2

Front 111

which elimination reaction favors weak bases?

Back 111

sn1 because bases does not appear in rate equation!

Front 112

which reactions have the exact same first step?

Back 112

sn1 and e1 -formation of a carbocation

same intermediate! =carbocation

Front 113

how do sn1 and e1 reactions differ?

Back 113

by what happens to the carbocation after it's formation

Front 114

what happens to the carbocation in the second step of an e1 reaction?

Back 114

base attacks a beta hydrogen (proton)

Front 115

what happens to the carbocation in the second step of an sn1 reaction?

Back 115

nucleophile attacks a carbon (from behind)

Front 116

what is the general scheme that occurs in an sn1 reaction?

Back 116

a carbocation forms is attacked by a nucleophile forming a substitution product.

Front 117

what is the general scheme that occurs in an e1 reaction?

Back 117

a carbocation is formed and then attacked by a base (removes a proton) creating a pi bond

Front 118

what conditions are favored by both sn1 and e1 reactions?

Back 118

a tertiary(3*) halide and WEAK nucleophile or base,

Front 119

what is the stereochemistry of E2 reaction?

Back 119

H & X must be anti! always! (called "anti-periplanar"

Front 120

what is it called when H and X are on the same side of a molecule?

Back 120

syn periplanar (cannot undergo E2 reactions)

Front 121

what type of conformation do anti periplanar arrangements have?

Back 121

staggered!

Front 122

what type of conformation so syn periplanar arrangements have?

Back 122

eclipsed!

Front 123

what is the most important factor that you can use to determine between e1 and e2?

Back 123

the strength of the base

Front 124

do strong bases favor e2 or e1?

Back 124

e2

Front 125

do weak bases favor e2 or e1?

Back 125

e1

Front 126

which is more useful, e2 or e1?

Back 126

e2 because e1 competes with sn1

Front 127

can e1 reactions occur with primary halides? can e2?

Back 127

not e1, but e2 yes

Front 128

how are alkynes formed?

Back 128

2 consecutive elimination reactions in which two pi bonds are formed (triple bond)

Front 129

what are the two general rules to folllow when determining if rxn is e1, e2, sn1 or sn2?

Back 129

[1] good nucleophiles that are weak bases favor substitution over elimination
[2] bulky, nonnucleophilic bases favor elimination over substitution