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Tutorials (5-9)

30 important questions on Tutorials (5-9)

What can you tell me about alcohols, phenols and ethers

Organic derivatives of water in which one or both of the water hydrogens are replaced by an organic group: H-O-H versus R-O-H, Ar-O-H and R-O-R

What can you tell me about alcohol classifications

Depends on the number of organic groups, R, bonded to the hydroxyl-bearing carbon

What can you tell me about the properties of alcohols/phenols

Alcohols have the same geometry around the oxygen atom as water
-> The C-O-H bound angle is approximately tetrahedral
-> The oxygen atom is sp3-hybridized

alcohols and phenols have high boiling points due to hydrogen bonding

alcohols and phenols are both weakly basic and weakly acidic
-> phenols are more acidic than alcohols because phenoxide anion is resonance-stabilized

What can you tell me about the weak bases and weak acids of alcohols

-> As weak bases they are reversibly protonated by strong acids to yield oxonium ions, ROH2+

-> As weak acids they dissociate slightly in dilute aqueous solution --> donating a proton to water, generating H3O+ and an alkoxide ion (RO-) or a phenoxide ion (ArO-)

What can you tell me about the acidity of alcohols/phenols?

The strength of an acid HA in water is expressed by an acidity constant Ka and by pKa
-> Compounds with larger pKa are less acidic --> less likely to donate H+
-> Compounds with smaller pKa are more acidic --> more likely to donate H+

What can you tell me about the reactions of alcohol: dehydration

Dehydration = elimination reaction (E1)
- The product is alkene
- Zaitsev's rule: yields the most stable alkene as the major product
- acid-catalyzed
- works well for

-> tertiary alcohols -> E1 mechanism

-> tertiary alcohols react fastest because they lead to tertiary cabocations
-> primary and secondary alcohols require much higher temperature for reaction

What can you tell me about the oxidation of alcohols?

- primary alcohols yield aldehydes or carboxylic acids
- secondary alcohols yield ketones
- tertiary alcohols do not normally react with most oxidizing agents

What can you tell me about the calculation of the oxidation state

- difference between number of valence electrons of the neutral atom and number of electrons that belong to it using the following rules:
1. Electrons in a bond between atoms of the same element are divided equally
2. Electrrons in a bond between atoms of different elements belong to the most electronegative atom
3. Electrrons in a lone pair belong only to the atom with the lone par

What can you tell me about the reactions of ethers

Ethers are unreactive to most common reagents
- no effect from mild acids, bases and nucleophiles on linear ethers
- only cleavage by very strong acids (HBr and HI)

stable compounds in nature

What can you tell me about Aldehydes (RCHO)

- most widely occurring of all compounds
- carbonyl group:
-> C and O are both sp2-hybridized
-> planar with bond angles close to 120º
- are easily oxidised to carboxylic acids

What can you tell me about ketones (R2CO)

- most widely occurring of all compounds
- carbonyl group:
-> C and O are both sp2-hybridized
-> planar with bond angles close to 120º
- are inert toward oxidation

What can you tell me about the structure and properties of carboxylic acids?

- carboxyl carbon is sp2-hybridized
- carboxylic acids are strongly associated because of hydrogen bonding
-> significantly incrreased bioling point
- most carboxylic acids exist as cyclic dimers

What can you tell me about the ionization of carboxylic acids

- carboxylic acids react with inorganic bases to give metal carboxylate salts
- carboxylic acids slightly ionize in water

What can you tell me about the acidity of carboxylic acids?

Carboxylic acids are much weaker acids than mineral acids but much stronger acids than alcohols

What can you tell me about carboxylic acids derivatives?

- compounds in which an acyl group is bonded to an electronegative atom or substituent that can act as a leaving group
- converted to parent carboxylic acid by hydrolysis reaction

What can you tell me about the conversion of carboxylic acids into esters?

- most useful reaction of carboxylic acids
- several methods for accomplishing the transformation
-> SN2 reaction with carboxylate anion with primary alkyl halide

What can you tell me about the Fischer esterification reaction?

Acid-catalyzed nucleophilic acyl substitution reaction of a carboxylic acid with an alcohol

What can you tell me about the rrole of acid in a Fischer esterfication reaction?

- direct nucleophilic acyl substitution of a carboxylic acid is difficult because the -OH group is a poor leaving group and the acid-base reaction with Nu
- reactivity is enhanced by:
-> protonating carbonyl oxygen of carboxyl group making the carbonyl carbon atom more electrophilic
-> converting -OH into better leaving group

What are the 4 steps of the mechanism of the Fischerr esterfication?

1. Protonation of the carbonyl oxygen activates the carboxylic acid
2. Toward nucleophilic attack by alcohol, yielding a tetrahedral intemediate
3. Transfe of a prroton from one oxygen atom to another yields a second ttetrahedral interrmediate and converrts the OH grrroup into a good leaving group
4. Loss of a proton and expulsion of H2O regenerates the acid catalyst and gives the ester product

What can you tell me about the conversion of amino acids into acids?

- base catalysed amide hydrolysis:
-> mechanism is very similar to hydrolysis of esters
-> seldom used: very slow (NH2 is very bad leavinng grroup)

- acid catlaysed aminde hydrolysis: impotrant for protein analysis

What can you tell me about the properties of amines?

- small amines (<5 carbons) are generally water-soluble
- amines form hydrogen bonds and are highly associated
-> H-bonding results in increased boiling points
- amines possess characteristic odors

What can you tell me about the basicity of amines?

- chemistry of amines dominated by lone pair on the nitrogen atom
-> lone pair makes amines both basic and nucleophilic

- weaker base: larger pKa
- stronger base: smaller pKa

amides are nonbasic
- amides do not undergo substantial protonation when treated with acids
- amides are poor nucleophiles
- nitrogen lone-pai electrons are stabilized through orbital overlap with the carbonyl group (resonance structure)

What can you tell me about the classification of monosaccharides?

- aldoses: aldehyde carbonylgroup + hydroxyl groups
- ketoses: ketone carbonyl group + hydroxyl groups

- more than one functional group
- one or more chirality centers, stereoisomers

What can you tell me about the fischer projection?

- method to project a tetrahedral carbon onto a flat surface
- tetrahedral carbon represented by two crossed lines
-> horizontal lines come out of the page (forewards)
-> vertical linnes go back into the page (backwards)

What can you tell me about hemiacetal formation?

- aldehydes and ketones undergo a rapid and reversible nucleophilic addition reaction with alcohols to form hemiacetals
- monosaccharides undergo intramolecular nucleophilic addition: carboxyl + hydroxyl group of one molecule -> cyclic hemiacetal

How do you go from Fischer projection -> Haworth projection?

1. Make 3D, rotate 90º
2. Cul it
3. Rotate around C2-C5-bond to form a six-membered ring
4. Nucleophilic addition, proton-loss and protonation

What can you tell me about the reactions of monosaccharides: glycoside formation?

- hemiacetals yield acetals upon treatment with an alcohol and an acid catalyst
- treatment of monosaccharides hemiacetals with an alcohol and acid catalyst yields an acetal, called glycoside

What can you tell me about the glycoside stability and abundance?

- glycoside are stable in neutral water and do not mutarotate
- glycoside hydrolyze back to free monosaccharide plus alcohol upon treatment with aqueous acid
- glycoside are abundant in nature -> cleaved by enzymes

What is an isoelectric point (pI)

- the pH at which the number of positive and negative charges on a protein (/ an amino acid) are equal
- depends on the structure of the amino acid

Which two types of lipids are there?

1. Those that contain ester linkage that can be hydrolyzed (includes fats and waxes)
2. Steriods which do not have ester linkage and cannot be hydrolyzed (includes cholesterol and other steroidal hormones)

The question on the page originate from the summary of the following study material:

ORC1

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