Section F Flashcards
What are the 6 fundamental chemical reaction types?
Electrophilic Addition, elimination, nucleophilic substitution, oxidation, nucleophilic carbonyl addition, nucleophilic acyl substitution
What chemical reaction occurs with alkenes (C=C)?
Electrophilic Addition
What chemical reactions occur with halides (F, Br, Cl)?
Nucleophilic substitution, elimination
What chemical reaction occur with alcohols (O-H)?
Nucleophilic substitution, elimination, oxidation
What chemical reaction occurs with ketones (C=O)?
Nucleophilic carbonyl addition
What chemical reaction occurs with aldehydes (COH)?
Oxidation, nucleophilic carbonyl addition
What chemical reaction occurs with carboxylic acids, acetals, esters and amides?
Nucleophilic acyl substitution
What reaction would we use to convert an alkene into an alkyl halide?
Electrophilic Addition
What reaction would we use to covert an alkyl halide into an alkene?
Elimination
What reaction would we use to convert an alkyl halide into an alcohol?
Nucleophilic substitution
What reaction would we use to convert an alcohol into a aldehyde/ketone?
Oxidation
What reaction would we use to convert an aldehyde/ketone into a hemiacetal/acetal/hemiketal/ketal?
Nucleophilic carbonyl addition
What reaction would we use to convert an aldehyde into a carboxylic acid?
Oxidation
What reaction would we use to convert a carboxylic acid into an ester/acid halide/amide?
Nucleophilic acyl substitution
What is important about nucleophilic substitution reactions?
They are reversible, same reaction can be used in either direction
Define electronegativity
The power of an atom in a molecule to attract electrons toward itself - results in a polarised bond with delta +ve and delta -ve partial charges
Define an electrophile
An electron loving molecule which has a +ve charge and is attracted to electron rich centres (seeks electrons)
What direction would a curved arrow point between an electrophile and nucleophile?
Tail of arrow would begin at nucleophile and end at electrophile (head)
When adding HCl to an alkene, what reaction occurs, what is the intermediate and what is the product?
Electrophilic Addition, Carbenium/Carbocation, alkyl halide (H and Cl bound to diff. carbons)
When adding H2O to an alkene, what is the process and product?
Electrophilic addition, electron density from C=C bond attracted to H+ from H2O, creates +ve charge on other C which H2O then attracted to, O of H2O is +ve so loses an H+, alcohol formed
What is the rule of Markovnikov?
When an unsymmetric reagent adds to an unsymmetric alkene, the electropositive part of the reagent bonds to the carbon of the double bond that has the greater number of hydrogen atoms attached to it.
What is the most stable carbocation?
R3C+, then R2HC+, then RH2C+ then H3C+ (least stable) - electrophilic addition proceeds in a way to involve the most stable carbocation
Define regioselective
If a reaction has a preference for 1 of 2+ stereoisomers (regioisomers)
What is cholesterol synthesised from?
Squalene
What is elimination the reverse of?
Electrophilic Addition
What is the general reaction for a nucleophilic substitution?
Nu: + R-L —> R-Nu + L-
What properties must nucleophiles and leaving groups have?
Nucleophile: electron excess (lone pair, charge), Leaving group: polarised carbon-L bond, stable as anion
What is the reaction for the extension of glucose?
SN: UDP-Glucose-Uridine + Glycogen (n) —> Uridine + Glycogen (n+1): glucose incorporated into glycogen
How many steps are in a bimolecular nucleophilic substitution (SN2)?
One step
How does the nucleophile attack in SN2?
Backside attack, causes umbrella flip
What is bound to reactant in transition state of SN2?
Both the nucleophile and leaving group are bound to carbon centre in transition state
What does the reaction rate depend on in SN2?
[Nu] and [Substrate]
What type of halide has the fastest reaction in SN2?
Primary halide has fastest reaction
How many enantiomers are formed in SN2?
Only one pure enantiomer is formed as reactions are stereospecific
How many steps are in a unimolecular nucleophilic substitution (SN1)?
Two steps, bond broken between carbon and leaving group before nucleophile comes in
What does the reaction rate depend on in SN1?
Only [Substrate]
What type of halide has the fastest reaction in SN1?
Tertiary Halide has fastest reaction
How many enantiomers are formed in SN1?
2 enantiomers formed, 50/50 mix of enantiomers -> racemisation
What type of nucleophilic substitution reaction has a rate retarded by polar protic solvents?
SN2 has a retarded rate whereas SN1 has an increased rate using polar solvents
Which type of nucleophilic substitution reaction is not dependent on [Nu]?
SN1 (only [Substrate] matters)
Which nucleophilic substitution reaction favours a neutral nucleophile?
SN1 favours a neutral nucleophile, SN2 favours an anion
What is an example of a good polar protic solvent?
H20 and EtOH
Are negative or neutral ions more nucleophilic?
Negative (Anions) more nucleophilic e.g. H2O
How does nucleophilicity vary down the periodic table?
Atoms become more nucleophilic as you go down the periodic table
What is the Geranyl Diphosphate -> Geranoil reaction an example of?
SN1 Nucleophillic substitution
What is an example of an SN2 reaction?
Norepinephrine + S-adenosylmethionine —> Epinephrine + S-adenosylhomocysteine
What 2 different types of elimination reactions are there?
E1 (two step) and E2 (one step)
Can an aldehyde be oxidised to a carboxylic acid?
Yes, but Ketones cannot
Is a primary alcohol or secondary alcohol more difficult to oxidise?
Primary alcohols are more difficult to oxidise, they are oxidised to aldehydes, whereas secondary alcohols are oxidised to ketones
What are secondary alcohols oxidised to?
Ketones
What are 2 oxidising agents & solutions?
K2Cr2O7 and H2SO4 (breathaliser), AgNO3 and NH3 (tollens)
What is the mechanism for oxidation?
Nucleophile attacks proton next to alcohol, electron density moves to form C=O bond OR nucleophile can attack alcoholic proton
What is the shape of the intermediate in nucleophilic carbonyl addition?
Tetrahedral
What type of nucleophile requires activation of the carbonyl group by acid catalysis?
Weak nucleophiles, create resonance stabilised carbocation with +ve charge swapping between C and O
What are chemist’s reducing agents?
LiALH4 and NaBH4 (& H+/H2O)
What are nature’s reducing agents?
NADH
What occurs during reduction of a C=O bond in Nucleophilic carbonyl addition?
nucleophile attacks +ve carbon, electron density from double bond moves onto O to make O- which then acts as a nucleophile for nearby hydrogen
What chemicals are used to convert a benzene ring with C=O bond to alcohol?
LiAlH4 and THF for first step, then H+ and H2O for second step
What is a hemiacetal/hemiketal?
Derived from an aldehyde/ketone where an alcohol group is added to the carbonyl group - COROH
How do you form a hemiacetal?
Nucleophilic attack of an alcohol
What is Keto-Enol tautomerism?
Chemical equilibrium between keto form (ketone/aldehyde) and an enol form (alcohol w/ double bond)
What are the 3 steps in the Aldol Condensation?
Enolate formation, nucleophilic addition, protonation
What are the reactions and products used in the Aldol condensation?
Acetaldehyde is reactant and 3-hydroxybutanal is the product, OH- ions used as catalyst
