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exam 2 Flashcards

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1
Q

which atoms are electron rich in a carboxylic acid?

A

the oxygen atoms (electron withdrawing because they are more electronegative)

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2
Q

which bond is shorter, a C-O in an alcohol or the C-O single bond in a carboxylic acid and why?

A

C-O in carboxylic acid is shorter because it is sp2 hybridized. C-O in alcohol is sp3 hybridized. greater percent s-character = shorter bond length.

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3
Q

IUPAC name of carboxylic acid chain

A

change -e ending of parent chain to -oic acid

make COOH group be #1 & number the rest of the substituents accordingly

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4
Q

IUPAC name of a carboxylic acid ring

A

name the ring & add “carboxylic acid” to the end.

Make the carboxylic acid #1 & number the rest accordingly

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5
Q

how do you form the common name of a carboxylic acid?

A

Add -ic acid to the end of the common parent name

name substituents using alpha, beta, gamma, delta (alpha is 1st carbon after the COOH etc.)

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6
Q

what are the common parent names of carboxylic acids?

A 
1C = form-(ic acid)
2C = acet-(ic acid)
3C = propion-
4C = butyr-
5C = valer-
6C = capro-
cyclohexane ring = benzo-
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7
Q

how do you name a compound with 2 carboxylic groups using IUPAC?

A

add -dioic acid to the name of the parent alkane

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8
Q

how do you name a metal salt of carboxylate anion?

A

change the -ic acid ending of the carboxylic acid to -ate

name of metal cation + parent (common or IUPAC) + -ate

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9
Q

what are the physical properties of carboxylic acids?

A

higher boiling & melting points than other compounds of comparable molecular weights (dipole-dipole interactions from polar C-O and O-H bonds and intermolecular hydrogen bonding because H atom bonded to electronegative O atom)

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10
Q

what is the solubility of carboxylic acids?

A

soluble in organic solvents no matter what size
less than or equal to 5 C’s –> water soluble because they can H bond with H2O
greater than 5 C’s are water insoluble because nonpolar alkyl portion is too large to dissolve in polar H2O solvent (fatty acids - dissolve in a nonpolar fat-like environment)

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11
Q

what are the characteristic IR absorptions of a carboxylic acid?

A

C=O absorbs at about 1710cm-1 - usual region for carbonyl

O-H absorbs between 2500-3500 cm-1 - broad - sometimes obscures C-H peak at 3000 cm-1

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12
Q

what are the characteristic NMR absorptions of a carboxylic acid?

A

H NMR - highly deshielded OH proton absorbs somewhere between 10 & 12 ppm - farther downfield than all other absorptions of common organic compounds
protons on the alpha carbon are somewhat deshielded, so absorb around 2-2.5 ppm

C NMR - carbonyl absorption is highly deshielded - so appears at 170-210 ppm

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13
Q

how are carboxylic acids typically prepared & why?

A

typically prepared by oxidation reactions, because the carbonyl carbon is highly oxidized (has 3 C-O bonds - Oxidation is Loss of C-H bonds).

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14
Q

how can you make a carboxylic acid from a primary alcohol?

A

Na2Cr2O7, K2Cr2O7 or CrO3 in the presence of H2O and H2SO4

both C-H bonds of the carbon bonded to alcohol are replaced by C-O bonds (both H’s turn into a single double bonded O)

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15
Q

what is an alkyl benzene?

A

a benzene ring that has an alkyl group bonded to it

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16
Q

how do you form a carboxylic acid from an alkyl benzene?

A

oxidation reaction
must have at least one benzylic C-H bond
add KMnO4
benzoic acid is always the product regardless of the alkyl benzene used as starting material

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17
Q

how do you form a carboxylic acid from an alkyne?

A

oxidative cleavage:
can be done with internal and terminal alkynes
cleaved with ozone (O3)
add (1) O3 (2) H2O
with terminal alkynes, it makes one carboxylic acid and a CO2 molecule

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18
Q

what are the reactive sites on a carboxylic acid?

A

polar C-O and O-H bonds and the pi bond

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19
Q

carboxylic acids are ____ Bronsted-Lowry ____

A

strong Brønsted-Lowry acids

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20
Q

what products of an acid-base reaction does equilibrium favor?

A

the weaker acid and weaker base products

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21
Q

how does pKa relate to acid-base reactions?

A

an acid can be deprotonated by a base that has a conjugate acid with a higher pKa

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22
Q

why are carboxylic acids so strong?

A

deprotonation forms a resonance-stabilized conjugate base - a carboxylate anion

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23
Q

what acid is strongest; carboxylic acid, alcohol or phenol?

A

carboxylic acid is stronger than alcohol or phenol because its conjugate base is most effectively resonance stabilized
even though phenol has MORE resonance structures, the absolute number of resonance structures is not necessarily determinate of acid strength

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24
Q

how is the pKa of a carboxylic acid affected by nearby groups?

A

electron-withdrawing groups stabilize the conjugate base, and so make the carboxylic acid more acidic
electron-donating groups destabilize the conjugate base, and so make the carboxylic acid less acidic

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25
Q

how does number, electronegativity and location of substituents affect acidity?

A

the larger the number of electronegative substituents, the stronger the acid
the more electronegative the substituents, the stronger the acid
the closer the electron-withdrawing group to the COOH, the stronger the acid

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26
Q

what are electron donating groups on a benzene ring (starting with most activating)

A
  • NH2 (NHR, NR2)
  • OH
  • OR
  • NHCOR
  • R
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27
Q

what are electron-withdrawing groups on a benzene ring? starting with least deactivating

A
  • X (F, Cl, Br,I)
  • CHO
  • COR
  • COOR
  • COOH
  • CN
  • SO3H
  • NO2
  • N+R3
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28
Q

If a group is deactivating or activating, how does it affect acidity of a benzene ring?

A 
activating groups (electron-donating groups) make a benzoic acid less acidic
deactivating groups (electron-withdrawing groups) make a benzoic acid more acidic
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29
Q

what does it mean that a group is activating or deactivating?

A

activating groups donate electron density and activate a benzene ring towards electrophilic attack
deactivating groups withdraw electron density and deactivate a benzene ring towards electrophilic attack

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30
Q

what is the maximum number of hydrogens in a carbon chain?

A

2(n) + 2

n = number of carbons

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31
Q

what is the structure of benzene?

A

6 membered ring w/3 additional degrees of unsaturation
planar
all C-C bond lengths are equal

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32
Q

how many pi electrons does benzene have?

A

6

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33
Q

what is the geometry of the carbons in a benzene ring?

A

sp2 hybridized, trigonal planar with all bond angles 120 degrees

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34
Q

where is the electron density in a benzene ring?

A

above and below the ring of carbons (2 donuts)

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35
Q

what does benzene readily react with and why?

A

electrophiles because the 6 pi electrons make it electron rich

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36
Q

how do you name monosubstituted benzenes?

A

name the substituent and add benzene (ethyl benzene…)

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37
Q

what is toluene?

A

benzene ring with CH3

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38
Q

what is a benzene ring with CH3 common name?

A

toluene

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39
Q

what is phenol?

A

a benzene ring with an alcohol group (-OH)

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40
Q

what is the common name for a benzene ring with an alcohol group?

A

phenol

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41
Q

what is aniline?

A

a benzene ring with NH2 substituent

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42
Q

what is the common name for a benzene ring with NH2 substituent?

A

aniline

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43
Q

how do you name a disubstituted benzene?

A

ortho (next door to each other)
meta (one away from each other)
para (across from each other)
alphabetize the names of substituents preceding the word benzene (o-bromochlorobenzene or m-dibromobenzene)
or you can use numbers (IUPAC)
OR you can use a common root name plus the letter (p-bromotoluene)

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44
Q

how do you name a polysubstituted benzene?

A

number to give the lowest possible numbers around the ring
alphabetize the substituents
if it’s a common root, the substituent that comprises the common root is located at C1
(4-chloro-1-ethyl-2-propylbenzene / 2,5-dichloroanaline)

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45
Q

how do you name an aromatic ring as a substituent?

A

a benzene substituent (C6H5-) is a phenyl group (Ph-)

a benyl group has an extra CH2 group between benzene ring and carbon chain (C6H5CH2-)

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46
Q

what are characteristic spectroscopic absorptions of benzene derivatives?

A

IR absorptions: Csp2-H 3150-3000
C=C 1600, 1500

H NMR absorptions: aryl H (H on the benzene ring) 6.5-8 ppm (highly deshielded protons)
benzylic H’s (bonded to one C away from ring) 1.5-2.5 (somewhat deshielded Csp3-H)

C NMR absorptions: Csp2 of arenes 120-150 ppm

47
Q

what is an arene?

A

aromatic hydrocarbon

48
Q

what happens to a benzene in the presence of a Lewis acid?

A

substitution (NOT addition) - characteristic of aromatic compounds

49
Q

what are the criteria for a compound to be aromatic?

A
  1. molecule must by cyclic
  2. molecule must be planar (adjacent p orbitals must be aligned so that the pi electron density can be delocalized)
  3. molecule must be completely conjugated (must have a p orbital on every atom)
  4. molecule must satisfy Huckel’s rule & contain a particular number of pi electrons (4n + 2) n = 0, 1, 2 etc.
50
Q

what is an antiaromatic compound?

A

cyclic, planar, and completely conjugated compounds that contain 4n pi electrons - especially UNstable

51
Q

how can all compounds be classified in terms of aromaticity?

A
  1. aromatic
  2. antiaromatic
  3. not aromatic (nonaromatic)
52
Q

how does aromaticity relate to stability?

A

aromatic compounds are more stable than similar acyclic compounds having the same number of pi electrons
antiaromatic compounds are less stable than acyclic compounds having the same umber of pi electrons
a compound that is not aromatic is similar in stability to an acyclic compound having the same number of pi electrons

53
Q

how does H NMR spectroscopy indicate whether a compound is aromatic or not?

A

protons on sp2 hybridized carbons in aromatic hydrocarbon are highly deshielded & absorb at 6.5-8ppm
hydrocarbons that are not aromatic absorb at 4.5-6 ppm - typical of protons bonded to the C=C of an alkene

54
Q

what is benzaldehyde?

A

benzene ring with CHO substituent

55
Q

what is a benzene ring with a CHO substituent?

A

benzaldehyde

56
Q

what is benzoic acid?

A

benzene with COOH attached

57
Q

what is a benzene ring with COOH attached?

A

benzoic acid

58
Q

How do you tell if a heterocycle is aromatic?

A

count a nonbonded electron pair if it makes the ring aromatic in calculating 4n+2. Lone pairs on atoms already part of a multiple bond cannot be delocalized in a ring, so they are never counted in determining aromaticity.

59
Q

what are the 2 steps that happen in all electrophilic aromatic substitution reactions?

A
  1. addition of electrophile E+ to form resonance-stabilized carbocation
  2. deprotonation with base
60
Q

what is the mechanism of electrophilic aromatic substitution?

A
  1. addition of the electrophile (E+) forms new C-E bond using 2 pi electrons from the benzene ring, generating a carbocation. Intermediate is not aromatic, but it is resonance stabilized (3 resonance structures can be drawn. rate-determining step because aromaticity of benzene ring is lost.
  2. base (B:) removes proton from the carbon bearing electrophile, re-forming the aromatic ring. Fast step because aromaticity is restored.
61
Q

where is the positive charge located in the carbocation intermediate of an aromatic electrophilic substitution?

A

ortho or para to the new C-E bond

62
Q

What is halogenation of a benzene?

A

benzene reacts with Cl2 or Br2 in he presence of a Lewis acid catalyst (FeCl3 or FeBr3) to give the aryl halide, chlorobenzene or bromobenzene

63
Q

What is the mechanism of bromination of benzene?

A

1) Lewis acid-base reaction of Br2 with FeBr3 Br-Br+-Fe(-)Br3
2) addition of electrophile forms new C-Br bond & generates carbocation that is resonance stabilized (3 resonance structures). FeBr4- also formed & is used as base in step 3.
3) FeBr4- removes proton from the C bearing the Br, re-forming the aromatic ring. FeBr3 catalyst is regenerated.

64
Q

How do you form the electrophile for nitration and sulfonation?

A

strong acid (H2SO4)

65
Q

what is the mechanism for forming a nitronium ion for nitration?

A

H-:O:-NO2 + H-O-SO3H —> H2-O:(+)-NO2 + HSO4(-) —> H2:O: + N(+)O2 (electrophile)
(Lewis structure) :O:=N(+)=:O:

66
Q

what is the mechanism for formation of the electrophile in sulfonation?

A

+SO3H

SO3 (all 3 O’s double bonded to S) one of the double bonds attacks H on H-OSO3H—> +SO3H (electrophile) + HSO4(-)

67
Q

How do you make nitrobenzene?

A

benzene + HNO3 and H2SO4 —> benzene + NO2 added onto the ring

68
Q

How do you make benzenesulfonic acid?

A

sulfonation:

benzene ring + SO3 and H2SO4 —> benzene ring with SO3H substituent

69
Q

what is formed in Friedel-Crafts alkylation?

A

alkyl benzene

transfers alkyl group from one atom to another (from Cl to benzene)

70
Q

What is the general reaction of Friedel-Crafts alkylation?

A

benzene ring + RCl and AlCl3 —> alkyl benzene (benzene ring with R group substituent) + HCl

71
Q

what is Friedel-Crafts acylation?

A

benzene ring treated with acid chloride (RCOCl) and AlCl3 to form a ketone

72
Q

what is the new group bonded to a benzene ring called in Friedel Crafts acylation?

A

acyl group

73
Q

what is acylation?

A

transfer of one acyl group from one atom to another

74
Q

How is the electrophile formed in a Friedel-Crafts Alkylation?

A

1degree RCl make Lewis acid-base complex serves as the electrophile
secondary and tertiary RCl, the Lewis acid-base complex reacts further to give a secondary or tertiary carbocation which serves as the electrophile. Carbocation formation ONLY occurs with secondary and tertiary alkyl chlorides

75
Q

What is the mechanism of a Friedel-Crafts Alkylation using a tertiary carbocation?

A

1) addition of the electrophile (tertiary carbocation) forms a new C-C bond (3 resonance structures)
2) AlCl4- removes a proton on the carbon bearing the new substituent, reforming the aromatic ring + HCl + AlCl3

76
Q

how is the electrophile formed in Friedel-Crafts Acylation?

A

AlCl3 ionizes the C-halogen bond of the acid chloride, forming positively charged carbon electrophile called an acylium ion (resonance stabilized)
AlCl3 grabs the Cl from the RCOCl, leaving R-C(+)=:O:R-Ctriplebond:O+ and AlCl4-

77
Q

what kind of halides do not react in Friedel-Crafts alkylation?

A

vinyl halides CH2=ChCl and aryl halides (benzene ring with halogen substituent)
to be reactive in a Fridel-Crafts alkylation reaction, the X must be bonded to an sp3 hybridized carbon atom

78
Q

which Friedel-Crafts reaction can involve rearrangement?

A

Friedel-Crafts Alkylation
when primary and secondary alkyl halides are used as starting materials, 1,2-hydride shift occurs to create more stable carbocation (to form tertiary carbocation)

79
Q

What else can be used (besides alkyl halides) as starting materials in Friedel-Crafts alkylation?

A 
any functional group that forms carbocations
most commonly alkenes (with strong acid - protonating alkene to form carbocation which is then the electrophile in the Friedel-Crafts alkylation)
and alcohol (with strong acid - protonating alcohol, losing the water, forming a carbocation)
acid: H2SO4 (H-OSO3H)
80
Q

What happens when a neutral O or N atom is bonded directly to a benzene ring?

A

Resonance dominates and net effect is electron donation

81
Q

What happen when a halogen is bonded directly to a benzene ring?

A

Inductive effect dominates and net effect is electron withdrawal

82
Q

What is toluene?

A

Benzene + CH3

83
Q

What reacts faster, toluene or benzene?

A

Toluene - electron donating CH3 activates the ring

Orthopara director

84
Q

What is nitrobenzene?

A

Benzene + NO2

85
Q

What reacts faster, benzene or nitrobenzene?

A

Benzene

Nitrobenzene is slower because NO2 is electron withdrawing and deactivates the ring

86
Q

List ring activators/deactivators in order from most activating to east

A 
NH2, NHR, NR2
OH
OR
NHCOR
R
F, Cl, Br, I (deactivate AND direct ortho para)
CHO
COR
COOR
COOH
CN
SO3H
NO2
N(+)R3
87
Q

What is the rule with ortho para directors (except for halogens)

A

All are R groups, or they have a non bonded electron pair on the atom bonded to the benzene ring

88
Q

What is the rule with meta directors (except for halogens)?

A

All have a full or partial positive charge on the atom bonded to the benzene ring

89
Q

Why do electron donating groups activate a benzene ring?

A

They stabilize a carbocation

Electron withdrawing groups destabilize a carbocation

90
Q

What is an amino group?

A

NH2

91
Q

What is a nitro group?

A

NO2

92
Q

Between acylation and alkylation, which can do it more than once?

A

Alkylation can go multiple times, acylation goes just once

93
Q

If there are 2 groups on a ring, where does the third go?

A

Directed by the most activating group

94
Q

How do you add a halogen to a benzene ring?

A

add a strong activating substituent, then X2 with FeX3 (Br and Cl = X)
substitution will occur at all H’s ortho and para to NH2 and OH groups

95
Q

How do you add just on Br to an activated benzene ring?

A

add Br2 alone with no catalyst. It will form a mixture of ortho and para products

96
Q

what is a benzylic C-H bond?

A

a H bonded to a C that is a substituent of a benzene ring

97
Q

Are benzylic C-H bonds stronger or weaker than most other sp3 hybridized C-H bonds?

A

weaker

because resonance-stabilized benzylic radical (5 resonance structures)

98
Q

What is benzylic bromination?

A

halogenation at the benzylic position on a benzene ring

99
Q

what is the mechanism for benzylic bromination?

A

1) Br2 + heat or light - cleaves Br-Br into to Br. radicals
2) one radical reacts & a new radical is formed (H-Br and radical on benzyl C - resonance stabilized)
3) radical C cleaves another Br2 molecule to add Br to the benzylic C and form another Br radical

100
Q

What are the 2 different reactions with Br2 that an alkyl benzene undergoes?

A 
ionic conditions (+FeBr3) - aromatic substitution ortho para isomers
radical conditions (+ heat or light): substitution of H by Br at benzylic carbon of alkyl group
101
Q

How do you go from a haloalkane to an alkene?

A

K+-OC(CH3)3 strong bulky base (E2)

102
Q

How do you reduce an aryl ketone to an alkyl benzene?

A

add Zn(Hg) + HCl
or NH2NH2 + -OH
replaces both C-O bonds with C-H bonds
needs heat

103
Q

What are two different ways to introduce an alkyl group on a benzene ring?

A

Friedel-Crafts alkylation (RCl and AlCl3) one step

Friedel-Crafts acylation (RCOCl and AlCl3) followed by reduction (Zn(Hg) + HCl) 2 step

104
Q

How do you add a nitro group to benzene?

A

HNO3 and H2SO4

105
Q

How do you reduce a nitro group on a benzene?

A

H2 and Pd-C catalyst — turns the NO2 group into an NH2 group (aniline)

106
Q

How do you name an ether substituent?

A

name the alkyl group + O atom as alkoxy substituent by changing the -yl ending of the alkyl group to -oxy (i.e. methoxy CH3O- ethoxy CH3CH2O-)

107
Q

What is the common name for ethanedioic acid?

A

oxalic acid

108
Q

what is the common name for butanedioic acid?

A

succinic acid

109
Q

what is the common name for propanedioic acid?

A

malonic acid

110
Q

rank in order of stability:

phenoxide, ethoxide, acetate

A

acetate is most stable (2 electronegative O atoms to delocalize negative charge)
then phenoxide (only 1 electronegative O atom, even though it has 5 resonance structures)
least stable is ethoxide (conjugate base of ethanol)
phenoxide is conjugate base of phenol

111
Q

how do you make a carboxylic acid?

A

from an alcohol, add K2Cr2O7 + H+ + H2O

112
Q

how do you make an alcohol from a haloalkane?

A

add OH- (substitution reaction)

113
Q

how do you make a haloalkane from an alkane?

A

add Cl2 or Br2 + heat or light (radical substitution)

114
Q

how do you make a haloalkane from an alkyne?

A

H2 + Pd or Pt

Organic Chemistry (6 decks)

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