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Organic Chem > Chapter 4: Organic Reactions > Flashcards

Chapter 4: Organic Reactions Flashcards

1
Q

Lewis acid (4)

A

any species (molecule or ion) that can accept a pair of electrons

(an electron acceptor in the formation of a covalent bond)

tend to be electrophiles

often positively charged atoms

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2
Q

Lewis base (4)

A

any species (molecule or ion) that can donate a pair of electrons

(an electron donor in the formation of a covalent bond)

tend to be nucleophiles

often anions (negative charge)

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3
Q

coordinate covalent bonds

A

covalent bonds in which both electrons in the bond came from the same starting atom (the Lewis base)

formed when Lewis acids and bases interact

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4
Q

Bronsted-Lowry acid

A

any species that can donate a proton (H+) to another molecule

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5
Q

Bronsted Lowry base

A

any species that can accept a proton (H+) from another molecule

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6
Q

amphoteric molecules

A

can act as either a Bronsted-Lowry acid or base, depending on reaction conditions

(ex. H2O can donate H+ to become OH- or accept H+ to become H3O+)

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7
Q

acid dissociation constant (Ka)

A

measures the strength of an acid in solution

the equilibrium constant corresponding to the dissociation of and acid (HA) into H + A

(larger Ka = stronger acid)

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8
Q

pka

A

pKa = - log (Ka)

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9
Q

small or negative pKa = ______

A

acidic molecules

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10
Q

large pKa = ______

A

basic molecules

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11
Q

strong acids have a pKA value of:

A

less than -2

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12
Q

weak acids have a pKA value of:

A

between -2 and 20

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13
Q

strong acids __________ in aqueous solution

A

dissociate completely

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14
Q

pKa trends in the periodic table

A
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15
Q

pka values for common functional groups:

list the acids from weakest to strongest

A
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16
Q

as bond strength decreases, acidity _______

A

increases

note: bond strength increases down the periodic table

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17
Q

the more electronegative an atom, the _______ the acidity

A

higher

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18
Q

doe bond strength or electronegativity take precedence when the 2 trends oppose each other?

A

bond strength

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19
Q

functional groups that act as acids

A

alcohols, aldehydes and ketones, carboxylic acids and most carboxylic acid derivatives

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20
Q

functional groups that act as bases

A

amines and amides

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21
Q

an acid-base reaction will proceed if the conjugate products are _______ than the reactants

A

weaker (less reactive, more stable)

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22
Q

nucleophiles

A

“nucleus-loving” species (nucleus is + charge so these species have a region of full or partial negative charge)

contain lone pairs or pi bonds

have a region of high electron density

often carry a negative charge

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23
Q

good nucleophiles tend to be good ______ (acids or bases)

A

bases

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24
Q

nucleophilicity is determined by 4 major factors

A

charge: ⇡ electron density (more negative charge) = ⇡ nucleophilicity

electronegativity = ⇡ electronegativity = ⇣ nucleophilicity

steric hindrance: bulkier molecules = less nucleophilic

solvent: protic solvens hinder nucleophilicity

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25
Q

polar protic solvents

A

contain at least one hydrogen atom connected directly to an electronegative atom

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26
Q

in polar protic solvents, Nucleophilicity increases ______ (up/down) the periodic table

A

down

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27
Q

in protic solvents, nucleophilicity decreases in the following order:

(4 halogens)

A

I- > Br- > Cl- > F-

28
Q

in protic solvents, nucleophilicity decreases in the following order:

(4 halogens)

A

F- > Cl- > Br- > I-

29
Q

polar aprotic solvents

A

have a medium range of polarity

can have hydrogen atoms somewhere in their structures, but no hydrogen atom is directly connected to an electronegative atom

30
Q

in polar aprotic solvents, Nucleophilicity increases ______ (up/down) the periodic table

A

up

31
Q

electrophiles

A

“electron-loving”

have a region of low electron density (positive or partial positive charge)

contain a positive charge or are positively polarized

more positive compounds are more electrophilic

accept an electron pair when forming new bonds with a nucleophile

32
Q

electrophiles almost always act as Lewis _____ (acids/bases)

A

acids

33
Q

list 4 functional groups that can act as electrophiles

A

alcohols, aldehydes, ketones, carboxylic acids (and their derivatives)

34
Q

leaving groups

A

molecules fragments that retain electrons after heterolysis

a species that leaves an electrophile with an electron pair

the leaving group must be able to stabilize the electrons it leaves with

35
Q

the best leaving groups can:

A

best stabilize the extra electrons

36
Q

_________ are good leaving groups

A

weak bases

37
Q

heterolytic reactions

A

a bond is broken and both electrons are given to one of the two products

the opposite of coordinate covalent bond formation

38
Q

what makes a good leaving group?

A

weak bases (the conjugate bases of strong acids)

39
Q

nucleophilic substitution reactions

A

a class of reactions in which one group is exchanged for another

a nucleophile forms a bond with a substrate carbon and a leaving group leaves

40
Q

SN1 reactions

A

unimolecular nucleophilic substitution reactions

step 1: loss of a leaving groups (rate determining step); a carbocation is formed

step 2: the nucleophile attacks the carbocation

attack from either side of the cation

41
Q

SN1 reaction rate

A

rate = k [substrate]

dependent upon the rate at which the leaving groups leaves

42
Q

SN2 rate

A

rate = K [substrate] [nucleophile]

note: substrate = R—leaving group

43
Q

SN2 reactions

A

bimolecular nucleophilic substitution reactions

step 1: loss of a leaving groups AND nucleophilic attack

“concerted” reaction

backside attack

“stereospecific” reaction: inversion causes a flip from R to S configuration or vice versa

44
Q

effect of degree of substitution on SN2 reaction rates

A

less sterically hindered electrophiles react more readily under SN2 conditions

45
Q

effect of degree of substitution on SN1 reaction rates

A

tertiary carbocations are more stable than secondary carbocations, which are more stable than primary carbocations

46
Q

how to determine SN1 vs sN2 based on substrate substitution

A
47
Q

how to determine SN1 vs sN2 based on the nucleophile (strong vs weak)

A
48
Q

how to determine SN1 vs sN2 based on the leaving group (good vs excellent)

A
49
Q

how to determine SN1 vs sN2 based on the solvent (polar aprotic vs protic)

A
50
Q

what does SN2 stand for?

A

S = substitution

N = nucleophilic

2 = bimolecular (number of species involved in the rate determining step)

51
Q

why are SN2 reactions called bimolecular

A

they have ONE step which involves TWO chemical entities

52
Q

redox reactions

A

the oxidation states of the reactants change

53
Q

oxidation state

A

an indicator of the hypothetical charge that an atom would have if all bonds were completely ionic

(note: don’t need to know how to assign oxidation states, just know the definition of oxidation/reduction)

54
Q

oxidation

A

an increase in oxidation state (loss of electrons)

usually involves decreasing bonds to hydrogen and increasing bonds to oxygen (or other heteroatoms)

55
Q

heteroatoms

A

atoms besides carbon and hydrogen

56
Q

oxidizing agent

A

the oxidizing agent accepts electrons and is itself reduced

tend to contain metals bonded to a large number of oxygen atoms

57
Q

reduction

A

a decrease in oxidation state (gain in electrons) assisted by reducing agents

usually means increasing bonds to hydrogen and decreasing bonds to other atoms

58
Q

reducing agents

A

donate electrons (are themselves oxidized)

have low electronegativity and ionization energy

often contain metals bonded to a large number of hydrogens

59
Q

chemoselectivity

A

the preferential reaction of one functional group in the presence of other functional groups

(a key skill is recognizing which reactions will occur by recognizing the reactive regions within a molecule!)

60
Q

steric protection

A
61
Q

what do nucleophiles do?

A

they provide a pair of electrons to form a new covalent bond

62
Q

imine

A

a compound with a nitrogen atom double bonded to a carbon atom

63
Q

enamines

A

contain both a double bond and a nitrogen-containing group

64
Q

condensation reaction

A

2 molecules are combined to form a single molecule, usually with the loss of a small molecule such as water

if water is lost, the reaction is also known as a dehydration synthesis

65
Q

imine formation

A
66
Q

cyanohydrins

A

a functional group in which a cyano and a hydroxy group are attached to the same carbon atom

form when hydrogen cyanide (HCN) reacts with aldehydes or ketones

cyanide functions as a nucleophile, attacking the carbonyl carbon

67
Q

alkyl halides

A

an alkane with one or more halogens attached (fluorine, chlorine, bromine, iodine)

Organic Chem (28 decks)

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