Organic II Flashcards
SN1 and SN2 are examples of what type of reaction?
Nucleophilic substitution
Between primary and tertiary halogenoalkanes, which occur via SN1 and SN2?
Why?
• Primary : SN2
• Tertiary : SN1
• SN1 depends on one slow step occurring. This is necessary for there to be space for the Nucleophile, as a tertiary halogenolakene has too much steric hinderance
Does SN1 or SN2 have a transition state?
How do you know this?
• SN2
• SN2 depends on the concentrations of both the halogenoalkane and the Nucleophile as there is one only step. This one step means everything happens at once, meaning at one point Carbon has 5 bonds.
What is more stable : carbocation intermediate or transition state, and which is SN1 and SN2?
• Carbocation intermediate is more stable
• Carbocation intermediate: SN1
• Transition state: SN2
Does SN1 or SN2 have two hills in the energy diagram?
What does the dip mean?
• SN1
• Carbocation intermediate
How to remember SN1 vs SN2 in terms of rate equation and primary vs tertiary?
• SN2 has two things in the rate equation so the Nucleophile is involved in the first step (has space to attack, primary)
• SN1 has one thing in the rate equation so only the halogenoalkane is involved in the first step, meaning it has to break off to make space (tertiary)
Does SN1 produce a racemic mixture ?
Why?
• Yes
• Proceeds via a planar carbocation intermediate, so the incoming Nucleophile can attack via either face of the compound
Does SN2 lead to a racemic mixture?
Why?
• No
• Nucleophile attacks while group leaves, so only one possible direction of attack leads to a single enantiomer being formed
Optical isomerism is a type of…
• stereoisomerism
Is the transition state in SN2 negative or positive?
How to represent ?
• Negative
• The double plus sign
What mechanism gives evidence for how optical activity arises in molecules?
• Nucleophilic addition
• Nucleophiles can attack a molecule with a carbonyl group from above or below the planar carbon-oxygen double bond
• This leads to mirror images
The two tests for aldehydes?
What does each thing act as ?
Method and positive results for each?
• Tollens reagant or Fehlings solution
• Oxidising agent
• Fehlings: warm tube and add drops, blue solution will make red precipitate
• Tollens: add, layer of silver will form on walls of test tube
All of the oxidation reactions involved in the production of carbonyl compounds from alcohols can be reversed via…
• reduction reactions
To reduce a carbonyl, you use …
What are the conditions?
This is what type of reaction?
The role of the molecule ?
• A reducing agent of lithium aluminium hydride (LiAlH4)
• Dry ether because it will react violently with water and alcohols
• Nucleophilic addition
• Provides the H- Nucleophile
How do you extend the carbon chain by one, starting from a carbonyl group?
This occurs via…
• Turn carbonyl into a hydroxynitrile by adding KCN/HCN
• Nucleophilic addition
Explain carbonyl + iodine reaction, how is it done and what is it called?
What else must be added and why?
What’s a positive result?
What compounds give a positive result?
• Iodoform reaction
• Iodine solution added to unknown sample, then enough sodium hydroxide (alkali) to remove the colour in the solution created by iodine
• formation of a pale yellow precipitate (triiodomethane, CHI3)
• aldehydes , ketones
What can be used as a qualitative test for the carbonyl functional group?
What’s a positive result?
2,4-DNPH
Yellow, orange or red precipitate
How can 2,4-DNPH be used to identify specific aldehydes and ketones (ethanal and methyl ketones)
• It is added to a compound so a precipitate forms
• The solid is then purified by recrystallisation to make orange crystals
• The melting points of the pure crystals can be compared with the melting points of the 2,4-DNPHs of all the common aldehydes and ketones
How can carboxylic acids be prepared?
Equation (for 2) and conditions ?
• Oxidation of primary alcohols or aldehydes under reflux using acidified potassium dichromate as the oxidising agent
• Hydrolysis of nitrile compounds
CH3CN + 2H2O + HCl —> CH3COOH + NH4Cl
Under reflux, dilute hydrochloric acid
Carboxylic acids are reduced to… using …
• Primary alcohols (aldehydes cannot be isolated as they are more reactive than carboxylic acids)
• Lithium aluminium hydride in dry ether
Carboxylic acids react with bases to make …
In a … reaction
• Salts
• Neutralisation
How can acyl chlorides be produced?
Equation?
• Carboxylic acids + phosphorus pentachloride, PCl5
• CH3COOH + PCl5 —> CH3COCl + POCl3 + HCl
How to make an ester from a carboxylic acid?
Conditions ?
Name of this?
Method for remembering reaction?
• Add alcohol
• Presence of acid catalyst, under reflux
• Esterification
• Take OH from acid and H from alcohol to make water and stick rest together
Two features of esters?
• Low boiling points
• Good solvents for polar molecules
Acyl chloride + water =
Carboxylic acid and HCl
Acyl chloride + Alcohol =
Ester and HCl
Acyl chloride + concentrated ammonia =
Amide + NH4Cl
Acyl chloride + Amine =
N-substituted Amide
Acyl chlorides + ammonia / primary amine : the link?
• With ammonia it’ll make a primary amide
• With a primary amine it’ll make a secondary amide
Acyl chlorides react via … reactions
The addition of a … leads to …
•Nucleophilic addition-elimination reactions
•Nucleophile
• The elimination of a product under aqueous conditions
How to hydrolyse esters?
• Add water and dilute acid
• OR add dilute alkali
Polyesters are formed from a reaction between
Makes a … linkage
• A dicarboxylic acid
• Diol
• Makes ester linkage
Hydrolysis of esters in acidic conditions makes…
• Alcohol
• Carboxylic acid
Hydrolysis of esters in alkaline conditions makes…
• Alcohol
• Carboxylate salt
Nucleophilic addition reactions occur with …
This mechanism shows…
• carbonyl compounds
• how optical activity arises in molecules as the nucleophile can attack from below or above the double bond, making mirror images
Products of partial oxidation of primary alcohol?
Products of full oxidation of primary alcohol?
Aldehyde and water
Carboxylic acid
Products of oxidation of secondary alcohol?
Ketone and water
