Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

MCAT Chemistry > Oxygen Containing Reactions > Flashcards

Oxygen Containing Reactions Flashcards

You may prefer our related Brainscape-certified flashcards:
MCAT flashcards Periodic Table flashcards Chemistry 101 flashcards AP® Chemistry flashcards Organic Chemistry 101 flashcards
1
Q

Nucelophiles

A

Molecules that tend to donate electrons to form new bonds
AKA Lewis bases
Some nucleophiles are strong Lewis bases, some are weak
E.g. alcohols and amines with common targets of carbonyls and phosphate groups
Lone pairs of electrons, pi-bonds, and sometimes even certain sigma bonds can act as nucleophiles

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

What happens when an alcohol attacks the carbonyl carbon of a carboxylic acid or derivate? When they attack a ketone or aldehyde?

A

Attacking a carbonyl carbon of carboxylic acid or derivate will form an ester
Attacking a ketone or aldehyde will form a hemiketal or hemiacetal

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

Is Nitrogen or Oxygen a better nucleophile?

A

Nitrogen is a better nucleophile
It shares electrons more readily, tends to bond well to Carbon, and doesn’t want to leave a bond
Oxygen is more electronegative, meaning it will form a weaker and more polar bond (unstable)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

What requirement does an alcohol or amine usually need to be a nucleophile?

A

Usually requires a basic or neutral solvent

Ask yourself when you see an alcohol or amine: “Is this the strongest nucleophile? If yes, where will it attack?”

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

Where will nucleophiles almost always attack on the MCAT?

A

A carbon atom
Carbons always form four bonds, though some may form double or triple bonds
Carbon must give up a pre-existing bond t make room for new bond

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

What types of atoms/molecules make good leaving groups?

A

Atoms with a greater number of electron shells, or those that have many resonance structures which allow distribution of charge, also weak bases
Make good leaving groups and poor nuclephiles
Leaving groups that leave as gases (CO2 or N2, think Citric Acid cycle release of CO2) leave solution and do not return, so do not compete with other nucleophiles
When two nucleophiles are involved, the better nucleophile will bond, the weaker will leave

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

How does the boiling point of an alcohol compare to similar hydrocarbons?

A

Boiling and melting points of alcohols are generally much higher than their similar size alkanes because of hydrogen bonding
Bp increases with molecular weight and decreases with branching for alcohols

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

What are three important reactions of alcohols?

A
  1. Nucleophilic reactions in which the alcohol will be the nucleophile (two lone pairs are exposed by bent shape of molecule, creating partial negative charge that causes alcohol to attack a positive or partial positive charge, considered electron-donating group)
  2. Can act as acids, losing their hydrogen
  3. Protonated alcohols can act as leaving groups
    Dependent on other chemicals with which it is being reacted
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

Rank the following molecules in order from least nucleophilic to most nucleophilic:

H2O, NH3, OH-, OR-, NH2-, CH3-, and R
C=O
O-

A

H2O < R < NH3 < OH- < OR- < NH2- < CH3-
C=O
O-

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

Why do alcohols typically act as nucelophiles?

A

Two lone pairs of electrons on Oxygen are exposed by the bent shape of molecule, creating a partial negative charge that causes the alcohol to attack a positive or partial positive charge

Considered electron-donating group

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

What are some strongly electron donating groups?

A

-O-
-OH
-NR2
Think of lone pairs and extra electron charge

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

What are some moderate to weak donating electron groups?

A

Weak: -R
Moderate: -OR

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

What are some strong electron-withdrawing groups?

A

O- -N+R3 -CCl3

-N+=O

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

What are some weak and moderate electron withdrawing groups?

A

Moderate: Ketone, Aldehyde, Ester, Carboxylic Acid (think about carbonyl C)
O=S=O
OH -C=-N (Carbon has partial positive)

Weak: -X (Halide)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

Rank the acidity of alcohols from primary to tertiary

A

Most acidic is methyl > primary alcohol > secondary alcohol > tertiary alcohol
Where tertiary alcohols are more basic

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

What reaction can alcohols undergo to become better leaving groups?

A

Can be converted to type of ester called a sulfonate (more specifically a tosylate or mesylate)
This can protect alcohols and prevent them from acting as an acid or nucleophile, or from undergoing other undesirable reactions
Following reaction, sulfonate can be converted back to an alcohol
Alcohol will be drawn to strongly electron withdrawing sulfur to form the sulfonate

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

What makes sulfonate ions good leaving groups?

A

Sulfur can form many bonds with its empty d orbitals, and so any negative charge is well-distributed
Sulfonate ions are therefore weka bases and excellent leaving groups
Do not require protonation to act as leaving group, which means they are useful for substitution reactions in pH neutral solvents
R
O=S=O
O-

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

Why is ether a good solvent?

A

Contains lone pairs, but cannot Hydrogen bond with itself, so its boiling point is roughly comparable to that of alkane with similar MW
Organic compounds tend to be more soluble in ethers than in alcohols because less hydrogen bonds to be broken for compound to dissolve
More nonpolar
‘Like dissolves like’
Ethers are relatively nonreactive
Can show up as a solvent for a substitution rxn or cleavage of the ether by HI or HBr to form corresponding alcohol and alkyl halide

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

Rank a hydroxy- carboxylic acid, an alcohol, an ether, and an alkane in order of highest boiling point

A

Lowest to highest
Alkane < ether < alcohol < hydroxy- carboxylic acid
Carboxylic acid can form most H-bonds

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

How does Nitrogen compare to Oxygen as a nucleophile and leaving group?

A

Nitrogen behaves similarly to Oxygen, but even better nucleophile and worse leaving group than Oxygen
Carbon and Nitrogen closer electronegativity, so N shares e- more readily with C and so C-N bonds are stronger, less polar, and less reactive than C-O bonds

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

What two reactions should you consider with amines?

A
  1. Nitrogen acts as a nucleophile where lone pair of e- attacks a positive charge
  2. Nitrogen can take on a fourth bond (becoming positively charged)
    Amines generally react as nucleophiles (react with aldehydes and ketones in addition rxns and carboxylic acids in substitution rxns)
    Ammonia and amines can act as bases
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

Electrophiles

A

Molecules with a tendency to accept electrons to form new chemical bonds
Targets of nuclephiles
Common electrophiles have: carbonyls- aldehydes, ketones, and carboxylic acids - due to partial positive charge on carbonyl carbon
Carbohydrates and lipids are good examples

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

What should you think when you see a carbonyl?

A

Carbon double bonded to an oxygen
Think about planar stereochemistry: leaves open space above and below, reducing steric hindrance and making it more receptive to attack
Polarity: partial negative charge on Oxygen (easily protonated), partial positive charge on carbon
Excellent electrophiles

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

What are the most reactive carbonyls?

A

Acyl chlorides
Chloride pulls electron density away from already partially positive carbon
Nitrogen in an aide donates electron density to partially positive carbonyl carbon (stabilizes carbonyl)
Amide is the least reactive carboxylic acid derivative
In multiple carbonyl molecules, most reactive is target of nucleophile

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
Q

What are the categories of carbonyls when it comes to nucleophilic reactions?

A
  1. Those with a good leaving group. Undergo nucleophilic substitution
  2. Those without a good leaving group. Undergo nucleophilic addition reaction
    - can be the case when carbonyl carbon is bonded to only hydrogens or carbons
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
26
Q

What groups are likely to act as leaving groups for nucleophilic substitution reactions with carbonyls on the MCAT?

A

With acyl chlorides, the chloride ion is likely to leave
With esters, the OR group is likely to leave
In amides, the nitrogen will stay and the oxygen originally double bonded to carbon leaves
Aldehydes and ketones do not have a good leaving group- tend to undergo addition rxns (nucleophile likely to attack from both sides -> racemic mixture)
- Stereospecific rxns can occur with bulky group hindering approach of nucleophile from one side of carbonyl (rings)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
27
Q

What is the trend of reactivity of the following carbonyls?

Acid anhydride, acid halide, aldehyde, amide, carboxylic acid, ester, and ketone

A

Amide < carboxylic acid < acid anhydride = ester < ketone < aldehyde < acid halide
Acyl halides have halide anion leaving groups, very stable (charge and size)
Anhydrides have carboxylate anion leaving groups, very stable
Esters have alkoxide anion leaving groups, not very stable
Amides have amide anion leaving groups, (NH2-), not stable of all in solution

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
28
Q

What are two common reactions for a carboxylic acid?

A

Can act either as an acid, losing a proton
OR can act as a substrate attacked by nucleophiles in substitution reactions
Planar quality of carboxylic acid makes it vulnerable to nucleophilic attack (hydroxyl can be protonated to make a better leaving group)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
29
Q

Aliphatic acids

A

Carboxylic acids where the R group is alkyl group

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
30
Q

What are the salts of carboxylic acids named?

A

Named with suffix -ate which replaces the -ic (OR -oic)
E.g. acetic acid to _ acetate
Acetate abbreviated as -Oac
Salt of acetic acid: Sodium ethanoate or Sodium acetate

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
31
Q

How would you describe the boiling point of carboxylic acids?

A

Can form two strong hydrogen bonds with other molecules, forming dimers
Dimers significantly increase boiling point of carboxylic acids by effectively doubling the molecular weight of molecules leaving liquid phase

Saturated carboxylic acids with more than 8 carbons are generally solids, double bonds in unsaturated carboxylic acids impede crystal lattice, lowering melting point

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
32
Q

What carboxylic acids are miscible in water?

A

Carboxylic acids with four carbons or fewer
Five or more carbons become increasingly less soluble and 10 C are insoluble in water
Soluble in most nonpolar solvents bc able to solvate in dimer form w/o H bonding being disrupted

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
33
Q

How do carboxylic acids compare in acid strength to organic acids?

A

Very strong, conjugate base is stabilized by resonance
Electron withdrawing groups on alpha-Carbon help to further stabilize conjugate base (increases acidity of corresponding carboxylic acid)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
34
Q

What type of organic chemistry functional groups do fatty acids have?

A

Carboxylic acid at one end and carbon chain of 12-24 carbons in length
Relatively insoluble in blood and carrie in lipoproteins to cells throughout the body
COOH at one end allows fatty acid to attach to glycerol to create a triglyceride

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
35
Q

What is a general rule of thumb for the products of nucleophilic substitution reactions with carboxylic acids?

A

More reactive acyl derivatives can be made easily into less reactive ones, but not the other way around
Acyl chloride can be used to make an ester, but ester cannot be used to make an acyl chloride

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
36
Q

How can carboxylic acid derivatives be converted to carboxylic acids?

A

Through hydrolysis
Can occur in either acidic conditions (yielding the acid) or basic conditions (yielding carboxylate anion)
Hydrolysis of amides is only possible under extreme chemical conditions (high temperature, strong acid)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
37
Q

How are acyl chlorides typically synthesized?

A

Acyl chloride: Carboxylic acid has been replaced by a halide
Commonly synthesized with inorganic acid chlorides like SOCl2, PCl3, and PCl5 (react with carboxylic acids by nucleophilic substitution)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
38
Q

What is the leaving group of an anhydride?

A

Leaving group is a carboxylate ion

Nucleophilic stubstitution with an anhydride is commonly used to synthesize an ester or amide

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
39
Q

What type of reaction can produce an ester?

A

Alcohol has undergone nucleophilic substitution with a carboxylic acid
Catalyzed with a strong acid to protonate the hydroxyl on the carboxylic acid, however strong acids also catalyze reverse reaction so yield is usually low
Yield can be adjusted by using Le Chatelier’s principle with excess of H2O or alcohol
End of ester name is the carboxylate salt

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
40
Q

Transesterification

A

Alcohol undergoes reaction withe ester where one alkoxy group is substituted for another in ester
Equilibrium established and products adjusted by using excess of water or alkoxy group
To protect alkoxy on ester in other reactions, can use excess of corresponding alcohol to prevent transesterification

41
Q

Lactones

A 
Cyclic esters
Formed by an intramolecular reaction between an alcohol (nucleophile) and a carboxylic acid (electrophile) on the same carbon chain
Functional group in an important class of antibiotics called macrolides
42
Q

How are amides formed?

A

Amine, acting as nucleophile, substittues at the carbonyl of a carboxylic acid or one of its derivatives
Amides with no substituents on the nitrogen are primary, amides with one substitutent are secondary, and with two substituents are tertiary
If amide is under nucleophilic attack, the C-N bond is strong, so oxygen in C=O bond can be repeatedly protonated and become leaving group

43
Q

How are peptide bonds catalyzed?

A

Bond in Carbon-Nitrogen backbone of proteins
Nitrogen on one amino acid attacks the carbonyl carbon of the carboxylic acid on another amino acid creating an amide (peptide bond)
Ribosomes catalyze this reaction

44
Q

Lactams

A

Cyclic amides that can be formed via intramolecular reactions
Unstable in small ring sizes because of ring strain
Beta-lactams, which are found in several types of antibiotics, nucleophiles can easily react with their four member ring
Transpeptidase, which forms peptidoglycan in bacteria attacks the carbonyl on the lactam in penicillin with a hydroxyl in a nucleophilic substitution, irreversibly binding it to penicillin and rendering it ineffective

45
Q

What is the boiling point of aldehydes and ketones?

A

Aldehydes and ketones cannot H bond with themselves, but they can H bond with other molecules where a H is bonded to an F, O, or N
Therefore, bp is higher than alkanes with similar MW and less than corresponding alcohols
Aldehydes and ketones with up to four carbons are soluble

46
Q

Keto-enol Tautomerization

A

Shift from a carbonyl (keto) to an alkane with an alcohol (enol)
Achieved by deprotonation of the alpha-carbon and protonation of the carbonyl oxygen
Both tautomers exist at room temp, but carbonyl is favored
Reaction at equilibrium, rate of reaction can be increased by catalyst (acid or base)
Ketone in basic condition produces deprotonated enol or enolate (phosphoenolpyruvate, PEP is enolate in glycolysis)

47
Q

What governs the conversion between a kinetic enolate and thermodynamic enolate in an asymmetric ketones?

A

Asymmetric ketones mean the carbon chain on one side is not the same as the carbon chain on the other side, can form two enolates in tautomerization
Kinetic enolate: less substituted enolate, formed quickly by removal of one of three possible acidic alpha hydrogens, so kinetically favored
Thermodynamic enolate: more substituted double bond, more difficult to form (higher activation energy), but more thermodynamically stable

48
Q

How do thermodynamic vs. kinetic products compete?

A

Thermodynamic products always have higher activation energy, but are more thermodynamically stable
Kinetic products are always formed fast and so are kinetically favored, but less stable
Use of high heat will help get past activation energy in thermodynamic product
Use of bulky base in tautomerization favors kinetic enolate

49
Q

Describe the nucleophilic addition reaction for ketones and aldehydes under basic conditions.

A

In basic conditions, nucleophile attacks carbonyl carbon first, Carbon releases pi bond e- to Oxygen forming an alkoxide anion
Then the negative Oxygen gets protonated and former aldehyde or ketone is now an alcohol
Alkoxide or alcohol may be able to return to previous carbonyl form
Common nucleophiles: Alcohols, amines, organometallic reagents, hydrides, and nitriles

50
Q

Describe the nucleophilic addition to an aldehyde or ketone under acidic conditions.

A

Oxygen in carbonyl becomes protonated due to the acid in the solution.
Then, the nucleophile attacks the carbonyl carbon, and the pi e- of carbonyl carbon now move to Oxygen
Original aldehyde or ketone is now an alcohol

51
Q

Hemiacetals and Hemiketals

A

Hemiacetal: reaction of aldehyde with an alcohol to form a compound with carbon bonded to original R group, original hydrogen, original carbonyl Oxygen in form of OH and then new alcohol
Hemiketal: reaction of ketone with alcohol to form comopund with carbon bonded to both original R groups, original carbonyl Oxygen in form of OH, and new alcohol as fourth bond
Alcohol acts as nucleophile
Aldehydes and Ketones exist in equilibrium w/ hemiacetals and hemiketals which can be catalyzed by base or acid
Often too unstable to be isolated unless they exist in ring structures

52
Q

Acetals or Ketals

A

Formed by nucleophilic reaction of hemiacetal or hemiketal with another alcohol that can replace the OH group, catalyzed by acidic conditions (protonate hydroxyl)
Not easily returned to carbonyl form because OR bond is not easily broken to allow return of Oxygen to double bond with carbon
Good protecting groups when there is need to prevent aldehyde or ketone from reacting
Aldehydes and ketones are more reactive than anhydrides, carboxylic acids, esters and amides and will be attacked first by nucleophiles
Convert back to aldehyde or ketone through acid-catalyzed hydrolysis

53
Q

What is a natural example of hemiacetals/ketals and acetals/ketals in the body?

A

Monosaccharides are hemiacetals and hemiketals, while polysaccharide chains with the glycosidic linkages are full acetals and ketals
Polysaccharides are stabilized and protected and they are called non-reducing sugars

54
Q

How do aldehydes and ketones react with amines?

A

React via nucleophilic addition of an amine to form imines and enamines
Amine attacks with lone pair of electrons at carbonyl carbon
Carbonyl oxygen protonated twice via acid catalysis in second step
Either formation of enamine with double bond between orginal carbonyl carbon and alpha carbon with secondary amine group OR formation of Nitrogen Carbon double bond to form imine
In both cases, water group leaves
Enamine is less stable because nitrogen withdraws electron density from C C double bond
Enamine is tautomer of imine
Only formed with primary or secondary amines

55
Q

Grignard Synthesis of Alcohol

A

Reaction of organometallic reagents with aldehydes or ketones via nucleophilic addition to form an alcohol
Organometallic reagents (Grignard reagents) are strongly basic and therefore more potent nucleophiles than even negatively charged Oxygen or Nitrogen
Possess highly polarized carbon-metal ionic bonds
RH2C-M+ where M represents metal
Makes new carbon-carbon bond, so alkane chain elongated
In second step, acid catalyzed to protonate oxygen
E.g. Carboplatin (chemotherapeutic drug) contains platinum atoms attached to carbon side chains and intercalates btwn DNA strands, preventing DNA replication

56
Q

Reduction Synthesis of alcohol

A

Use of hydride to synthesize alcohols, which occurs via nucleophilic addition
Hydrides (H-) react with carbonyl to form alcohol
Does not extend carbon skeleton (unlike Grignard synthesis)
Second step is acid catalyzed to protonate oxygen
H- ion such a strong base, too unstable to exist in isolation and therefore comes from hydride reagent, such as LiAlH4 and NaBH4
Both NaBH4 and LiAlH4 reduce aldehydes and ketones, but only LiAlH4 is strong enough to fully reduce carboxylic acids and esters and acetates to alcohols

57
Q

Nitriles

A

CN-
Nucleophiles that produce cyanohydrins (nitrile and alcohol attached to same carbon) when they attack carbonyl
Converts to carboxylic acid when exposed to water

58
Q

Phosphoric Acids

A

Phosphoric acid structure is a P double bounded to an oxygen and then with three additional hydroxyl substituents attached
When heated phosphoric acids form phosphoric anhydrides which has three phosphorous atoms (three phosphoric acid molecules)
- High energy bonds and serve as major form of energy in cell as adenosine triphosphate (ATP)
- Triphosphates in pH of 7 are negatively charged ions, so stable from nucleophilic attack
Phosphoric acids also react with alcohols to form esters

59
Q

What are rules to determine if compound has been oxidized or reduced?

A

Oxidation: increase in bonds to oxygen or halogen, loss of C-H bonds
Reduction: increase in bonds to hydrogen or R groups, loss of bonds to oxygen or halogen
Neither: addition or loss of H+, H2O, HX, etc.

60
Q

What reaction can convert an alcohol to an alkene?

A

Elimination Reaction

61
Q

What happens when you oxidize an alcohol?

A

Primary alcohols oxidize to aldehydes, which oxidize to carboxylic acids
Secondary alcohols oxidize to ketones
Tertiary alcohols- do not worry about

62
Q

What are some common oxidizing and reducing agents?

A

Oxidizing: K2Cr2O7, K2MnO4, H2CrO4 (strong: alcohols to COOH), O2, PCC (weaker: primary and secondary alcohols to aldehydes, ketones)
Reducing: LiAlH4, NaBH4, H2+ pressure

63
Q

How do most reduction reactions occur?

A

Hydride ion attacking a carbonyl carbon

64
Q

Decarboxylation

A

Oxidation of carboxylic acid to carbon dioxide gas
Usually exothermic, but activation energy is usually high, making reaction difficult to carry out
Activation energy lower when beta carbon is a carbonyl bc either anion intermediate is resonance stabilized or acid forms more stable cyclic intermediate
Citric Acid Cycle has two reactions that release CO2, generating NADH in the process

65
Q

Aldol Condensation

A

Carbonyl nucleophile attacks another carbonyl
Alpha-carbon can act as a nucleophile
New bond formed between alpha-carbon on one molecule (preserved carbonyl) and carbonyl carbon on other molecule (reduced to alcohol)
Condensation: water is removed at end o reaction
Aldehyde reacts with another aldehyde or ketone reacts with another ketone, or aldehyde reacts with ketone
Catalyzed by acid or base

66
Q

How does a base-catalyzed aldol condensation proceed?

A

Base removes alpha-hydrogen on the ketone or aldehyde to make the alpha carbon negatively charged (becomes enolate ion)
Enolate then acts as nucleophile, attacking carbonyl carbon of other aldehyde or ketone -> alkoxide ion (stronger base than OH-, so removes proton from water making aldol) -> aldol
Aldols are unstable and easily dehydrate by heat or a base to become an enal (aldehyde with an alkene at beta carbon, stabilized by conjugated double bonds)

67
Q

Aldol condensation examples

A

Fatty acid synthesis occurs by aldol condensation between an acetyl-CoA molecule and a growing fatty-acyl chain on Fatty Acid Synthase

One of the reactions of glycolysis
Reverse of reaction is retro-aldol which is what splits the ATP activated glucose in half

68
Q

How are nucleophilic carbonyl reactions used in biological molecules?

A

Carbohydrates, amino acids, nucleotides, and lipids are linked in chains through a nucleophilic carbonyl reaction
Formation of the bonds between macromolecules is called dehydration or condensation
-OH leaves one reactant and -H leaves the other, producing water as byproduct

69
Q

How is hydrolysis used in biological molecules?

A

Primary reaction used in digestion of macromolecules (carbohydrates, amino acids, nucleotides, and lipids)
Water is added to break bonds, key reagent
Enzymes required to efficiently make and break bonds between macromolecules

70
Q

Carbohydrates

A

Carbon chains with an alcohol on each carbon except for one, which has either an aldehyde or ketone attached in straight chain form
Ring formed when alcohol group on chiral carbon far from carbonyl attacks the carbonyl in a nucleophilic addition reaction, forming a hemiacetal
Carbohydrates exist predominantly in ring form in aqueous solution though equilibrium
Monosaccharides undergo intermolecular nucleophilic substitution reactions to form acetals (polysaccharides)

71
Q

Aldose

A

Carbohydrate that contains an aldehyde

72
Q

Ketose

A

Carbohydrate that contains a ketone

73
Q

How are carbohydrates classified based on stereochemistry?

A

Labeled D or L
Number all carbons in Fisher projections with number 1 at end of aldehyde or end of ketone closest to
If in Fisher projection, hydroxyl group on the highest numbered chiral carbon points to the right, carbohydrate is classified as D
If on the left, classified as L
Carbohydrates that have same structure, except for config around a single chiral center are epimers or stereoisomers

74
Q

What stereochemistry are most naturally produced carbohydrates?

A

D epimers
Enzymes involved in carbohydrate metabolism many times cannot recognize L carbohydrates
D for delicious

75
Q

Anomeric carbon

A

Formerly the carbonyl carbon, now the carbon attached to two oxygens in the ring structures of monosaccharides
Alcohol group on anomeric carbon may be pointing up or down in ring, resulting in either alpha or beta anomer
Alpha-glucose: hydroxyl group on anomeric carbon and methoxy group on carbon 6 are opposite
Beta-glucose: hydroxyl group and methoxy group on same side of carbon ring

76
Q

Glucose structure

A

Six-membered ring (including Oxygen) carbohydrate known as a glucopyranose
Can also be called an aldose, because possessed aldehyde in straight chain form
Can be alpha or beta, depending on where the methoxy on carbon 6 and hydroxyl group on anomeric carbon are pointing relative to each other

77
Q

How is a sugar that is formed by an alcohol to create an acetal named?

A

Given names that end in -oside
E.g. if hydroxyl group on anomeric carbon in glucose replaced by O-methyl group (alcohol), it is named methyl glucopyranoside
Group attached to anomeric carbon of a glycoside is called an aglycone

78
Q

Polysaccharides

A

Chains of monosaccharides
Glycosides (nucleophilic alcohol on anomeric carbon) where aglycone is another sugar
Linkages are called glycosidic linkages
Linkages formed between two reducing sugars in dehydration reaction

79
Q

Glycosidic linkages

A

Linkage between two sugars in a polysaccharide where aglycone on one monosaccharide is the next sugar
Named by noting the numbers of carbons involved in the bond
1,4’ link is when 1-carbon of one sugar and 4-carbon of next sugar linked
Anomeric carbons in bond usually includes anomeric config (alpha or beta)
Three common bond arrangements: 1,4’ link, 1,6’ link, and 1,1’ link

80
Q

What glycosidic linkages do humans have trouble breaking down?

A

Humans do not have the enzyme necessary to break beta-1,4’ linkages in cellulose
Some adult humans lack enzyme to break beta-1,4’ galactosidic linkage in lactose (lactose intolerance)

81
Q

Sucrose

A

1,1’ glycosidic linkage between glucose and fructose
Linkage is alpha wrt glucose and beta wrt fructose
More accurately called 1,2’ linkage because anomeric carbon on fructose in numbered 2, not 1 like glucose

82
Q

Maltose

A

Alpha-1,4’ glycosidic linkage between two glucose molecules

83
Q

Lactose

A

Beta-1,4’ galactosidic linkage between galactose and glucose

84
Q

Cellulose

A

Polysaccharide produced in plants

Contains beta-1,4’ glycosidic linkage between chain of glucose molecules

85
Q

Amylose (Starch)

A

Polysaccharide

Contains alpha-1,4’ glycosidic linkage between a china of glucose molecules

86
Q

Amylopectin

A

Alpha-1,4’ glycosidic linkage chain between glucose molecules
Branching with alpha-1,6’ glucosidic linkages forming the branches

87
Q

Glycogen

A

Alpha-1,4’ glycosidic linkages between chain of glucose molecules
Branches with alpha-1,6’ glucosidic linkages

88
Q

How are peptide bonds formed?

A

Amine on one amino acid acts as nucleophile to attack carbonyl carbon of carboxylic acid on another amino acid
Forms peptide or amide bond
-OH is leaving group

89
Q

What is the absolute configuration of amino acids?

A

All are S around central carbon, except for cysteine which is R (priority of sulfur R group) and glycine which is not chiral
Amino acids found in body are referred to as L amino acids

90
Q

Gabriel Synthesis

A
  1. Nitrogen protected in phathalimide to prevent additional alkylation. Nitrogen acts as nucleophile and substitutes bromide on diethyl-bromomalonate
  2. Hydrogen leaves middle carbon of diethyl-bromomalonate which makes carbon carbanion (nucleophilic) stabilized by COOH on either side
  3. Nucleophilic carbon undergoes nucleophilic substitution with new alkyl halide, adding R group of amino acid
  4. Nitrogen hydrolyzed from phthalimide by acid and water to create NH2 amino group
  5. Decarboxylation of second COOH in acid with heat to form amino acid
91
Q

Strecker Synthesis

A
  1. Aldehyde mixed with potassium cynaide and ammonium chloride. Cyanide acts as nucleophile toward carbonyl -> hydroxynitrile
  2. Nitrogen better nucleophile than oxygen, and acid protonates alcohol group, so ammonium attacks hydroxynitrile and hydroxy leaves as water -> aminonitrile
  3. Strong acid in water protonates nitrile group, turning back into COOH -> amino acid
    R group on aldehyde becomes R group in amino acid
92
Q

Fatty Acid

A

Long, even-numbered carbon chains with a carboxylic acid group at one end
Amphipathic, meaning they contain a hydrophobic and hydrophilic end
Hydrophobic carbon chain predominates, so fatty acids are nonpolar
The pKa of most fatty acids is ~4.5, so fatty acids exist in deprotonated anion form in cellular environment

93
Q

Triglycerides

A

Macromolecules that consist of one glycerol molecule and three fatty acids
Fatty acid carboxylic acids are converted to esters
In lipogenesis, the hydroxyl groups on the glycerol perform nucleophilic attack on carbonyl of carboxylic acids, forming an ester bond
Breaking down triglycerides into fatty acids and glycerol is called lipolysis
- When catalyzed by base, called saponification, forms soap (fatty acid salts + glycerol)

94
Q

How do you refer to a specific carbon on a fatty acid?

A

Carbon adjacent to carbonyl carbon of fatty acid: alpha carbon
Carbon at opposite end of chain: omega carbon
Carbons in between can be referred to by designating number of carbons away from alpha or omega carbon
Third carbon from end -> omega-3 carbon

95
Q

Saturated and Unsaturated Fatty Acids

A

Saturated: carbon chains on fatty acids contain no double bonds
Unsaturated: carbon chains on fatty acids contain double bonds
- All naturally occurring double bonds in fatty acids are in cis config, trans were created in lab and do not easily break down (humans do not have enzymes to)

96
Q

Melting points of unsaturated vs. saturated fatty acids

A

Melting point tends to increase with molecular weight
Unsaturated fatty acids have lower melting point than saturated acids
Saturated fatty acids are more straight and solidify more easily
Unsaturated fatty acids have ‘kinks’ and do not solidify as easily

97
Q

Nucleic Acids

A

Phosphate groups of nucleotides behave similarly to carboxylic acids
P=O is chemically similar to C=O
-OH group of one nucleic acid (off of 3-carbon) creates anhydride bonds with phosphate group of another (off of 5-carbon) to form phosphodiester backbone of RNA and DNA
Hydroxyl on Phosphate acts as leaving group, making it a nucleophilic substitution reaction

98
Q

Hydrolysis of Phosphoanhydride bond (ATP to ADP)

A

Water acts as nucleophile to one of the phosphate groups

An inorganic phosphate is released with a hydroxyl group off of it and ADP is produced from ATP

99
Q

Tollens Test

A

Gives a silver mirror when reacting with reducing sugars
Reducing sugars are hemiacetals in their ring form and either aldehydes or ketones in their straight-chain form
Acetals do not open easily because they contain a blocking group

MCAT Chemistry (8 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions