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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
polar protic solvents
contain at least one hydrogen atom connected directly to an electronegative atom
26
in polar **protic** solvents, Nucleophilicity increases ______ (up/down) the periodic table
down
27
in **protic** solvents, nucleophilicity decreases in the following order: *(4 halogens)*
I- \> Br- \> Cl- \> F-
28
in **protic** solvents, nucleophilicity decreases in the following order: *(4 halogens)*
F- \> Cl- \> Br- \> I-
29
polar aprotic solvents
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
in polar **aprotic** solvents, Nucleophilicity increases ______ (up/down) the periodic table
up
31
electrophiles
**“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
electrophiles almost always act as Lewis _____ (acids/bases)
acids
33
list 4 functional groups that can act as electrophiles
alcohols, aldehydes, ketones, carboxylic acids (and their derivatives)
34
leaving groups
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
the best leaving groups can:
best stabilize the extra electrons
36
\_\_\_\_\_\_\_\_\_ are good leaving groups
weak bases
37
heterolytic reactions
a bond is broken and both electrons are given to one of the two products the opposite of coordinate covalent bond formation
38
what makes a good leaving group?
weak bases (the conjugate bases of strong acids)
39
nucleophilic **substitution reactions**
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
SN1 reactions
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
SN1 reaction rate
rate = k [substrate] dependent upon the rate at which the leaving groups leaves
42
SN2 rate
rate = K [substrate] [nucleophile] note: substrate = R—leaving group
43
SN2 reactions
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
effect of degree of substitution on **SN2** reaction rates
less sterically hindered electrophiles react more readily under SN2 conditions
45
effect of degree of substitution on **SN1** reaction rates
tertiary carbocations are more stable than secondary carbocations, which are more stable than primary carbocations
46
how to determine SN1 vs sN2 based on substrate substitution
47
how to determine SN1 vs sN2 based on the nucleophile (strong vs weak)
48
how to determine SN1 vs sN2 based on the leaving group (good vs excellent)
49
how to determine SN1 vs sN2 based on the solvent (polar aprotic vs protic)
50
what does SN2 stand for?
S = substitution N = nucleophilic 2 = bimolecular (number of species involved in the rate determining step)
51
why are SN2 reactions called bimolecular
they have ONE step which involves TWO chemical entities
52
redox reactions
the oxidation states of the reactants change
53
oxidation state
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
oxidation
an increase in oxidation state (loss of electrons) usually involves decreasing bonds to hydrogen and increasing bonds to oxygen (or other heteroatoms)
55
heteroatoms
atoms besides carbon and hydrogen
56
oxidizing agent
the oxidizing agent accepts electrons and is itself _reduced_ tend to contain metals bonded to a large number of oxygen atoms
57
reduction
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
reducing agents
donate electrons (are themselves oxidized) have low electronegativity and ionization energy often contain metals bonded to a large number of hydrogens
59
chemoselectivity
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
steric protection
61
what do nucleophiles do?
they provide a pair of electrons to form a new covalent bond
62
imine
a compound with a nitrogen atom double bonded to a carbon atom
63
enamines
contain both a double bond and a nitrogen-containing group
64
condensation reaction
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
imine formation
66
cyanohydrins
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
alkyl halides
an alkane with one or more halogens attached (fluorine, chlorine, bromine, iodine)

Organic Chem (28 decks)

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