Oxygen Containing Reactions

Question 1

Nucelophiles

Answer 1

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

Question 2

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

Answer 2

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

Question 3

Is Nitrogen or Oxygen a better nucleophile?

Answer 3

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)

Question 4

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

Answer 4

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?”

Question 5

Where will nucleophiles almost always attack on the MCAT?

Answer 5

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

Question 6

What types of atoms/molecules make good leaving groups?

Answer 6

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

Question 7

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

Answer 7

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

Question 8

What are three important reactions of alcohols?

Answer 8

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

Question 9

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

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

Answer 9

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

Question 10

Why do alcohols typically act as nucelophiles?

Answer 10

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

Question 11

What are some strongly electron donating groups?

Answer 11

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

Question 12

What are some moderate to weak donating electron groups?

Answer 12

Weak: -R
Moderate: -OR

Question 13

What are some strong electron-withdrawing groups?

Answer 13

O- -N+R3 -CCl3

-N+=O

Question 14

What are some weak and moderate electron withdrawing groups?

Answer 14

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

Weak: -X (Halide)

Question 15

Rank the acidity of alcohols from primary to tertiary

Answer 15

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

Question 16

What reaction can alcohols undergo to become better leaving groups?

Answer 16

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

Question 17

What makes sulfonate ions good leaving groups?

Answer 17

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-

Question 18

Why is ether a good solvent?

Answer 18

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

Question 19

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

Answer 19

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

Question 20

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

Answer 20

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

Question 21

What two reactions should you consider with amines?

Answer 21

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

Question 22

Electrophiles

Answer 22

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

Question 23

What should you think when you see a carbonyl?

Answer 23

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

Question 24

What are the most reactive carbonyls?

Answer 24

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

Question 25

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

Answer 25

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

Question 26

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

Answer 26

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)

Question 27

What is the trend of reactivity of the following carbonyls? | Acid anhydride, acid halide, aldehyde, amide, carboxylic acid, ester, and ketone

Answer 27

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

Question 28

What are two common reactions for a carboxylic acid?

Answer 28

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)

Question 29

Aliphatic acids

Answer 29

Carboxylic acids where the R group is alkyl group

Question 30

What are the salts of carboxylic acids named?

Answer 30

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

Question 31

How would you describe the boiling point of carboxylic acids?

Answer 31

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

Question 32

What carboxylic acids are miscible in water?

Answer 32

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

Question 33

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

Answer 33

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)

Question 34

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

Answer 34

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

Question 35

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

Answer 35

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

Question 36

How can carboxylic acid derivatives be converted to carboxylic acids?

Answer 36

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)

Question 37

How are acyl chlorides typically synthesized?

Answer 37

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)

Question 38

What is the leaving group of an anhydride?

Answer 38

Leaving group is a carboxylate ion | Nucleophilic stubstitution with an anhydride is commonly used to synthesize an ester or amide

Question 39

What type of reaction can produce an ester?

Answer 39

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

Question 40

Transesterification

Answer 40

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

Question 41

Lactones

Answer 41

``` 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 ```

Question 42

How are amides formed?

Answer 42

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

Question 43

How are peptide bonds catalyzed?

Answer 43

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

Question 44

Lactams

Answer 44

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

Question 45

What is the boiling point of aldehydes and ketones?

Answer 45

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

Question 46

Keto-enol Tautomerization

Answer 46

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)

Question 47

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

Answer 47

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

Question 48

How do thermodynamic vs. kinetic products compete?

Answer 48

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

Question 49

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

Answer 49

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

Question 50

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

Answer 50

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

Question 51

Hemiacetals and Hemiketals

Answer 51

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

Question 52

Acetals or Ketals

Answer 52

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

Question 53

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

Answer 53

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

Question 54

How do aldehydes and ketones react with amines?

Answer 54

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

Question 55

Grignard Synthesis of Alcohol

Answer 55

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

Question 56

Reduction Synthesis of alcohol

Answer 56

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

Question 57

Nitriles

Answer 57

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

Question 58

Phosphoric Acids

Answer 58

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

Question 59

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

Answer 59

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.

Question 60

What reaction can convert an alcohol to an alkene?

Answer 60

Elimination Reaction

Question 61

What happens when you oxidize an alcohol?

Answer 61

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

Question 62

What are some common oxidizing and reducing agents?

Answer 62

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

Question 63

How do most reduction reactions occur?

Answer 63

Hydride ion attacking a carbonyl carbon

Question 64

Decarboxylation

Answer 64

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

Question 65

Aldol Condensation

Answer 65

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

Question 66

How does a base-catalyzed aldol condensation proceed?

Answer 66

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)

Question 67

Aldol condensation examples

Answer 67

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

Question 68

How are nucleophilic carbonyl reactions used in biological molecules?

Answer 68

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

Question 69

How is hydrolysis used in biological molecules?

Answer 69

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

Question 70

Carbohydrates

Answer 70

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)

Question 71

Aldose

Answer 71

Carbohydrate that contains an aldehyde

Question 72

Ketose

Answer 72

Carbohydrate that contains a ketone

Question 73

How are carbohydrates classified based on stereochemistry?

Answer 73

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

Question 74

What stereochemistry are most naturally produced carbohydrates?

Answer 74

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

Question 75

Anomeric carbon

Answer 75

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

Question 76

Glucose structure

Answer 76

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

Question 77

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

Answer 77

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

Question 78

Polysaccharides

Answer 78

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

Question 79

Glycosidic linkages

Answer 79

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

Question 80

What glycosidic linkages do humans have trouble breaking down?

Answer 80

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)

Question 81

Sucrose

Answer 81

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

Question 82

Maltose

Answer 82

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

Question 83

Lactose

Answer 83

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

Question 84

Cellulose

Answer 84

Polysaccharide produced in plants | Contains beta-1,4’ glycosidic linkage between chain of glucose molecules

Question 85

Amylose (Starch)

Answer 85

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

Question 86

Amylopectin

Answer 86

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

Question 87

Glycogen

Answer 87

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

Question 88

How are peptide bonds formed?

Answer 88

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

Question 89

What is the absolute configuration of amino acids?

Answer 89

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

Question 90

Gabriel Synthesis

Answer 90

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

Question 91

Strecker Synthesis

Answer 91

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

Question 92

Fatty Acid

Answer 92

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

Question 93

Triglycerides

Answer 93

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)

Question 94

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

Answer 94

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

Question 95

Saturated and Unsaturated Fatty Acids

Answer 95

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)

Question 96

Melting points of unsaturated vs. saturated fatty acids

Answer 96

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

Question 97

Nucleic Acids

Answer 97

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

Question 98

Hydrolysis of Phosphoanhydride bond (ATP to ADP)

Answer 98

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

Question 99

Tollens Test

Answer 99

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