Reactions And Conditions (Organic II) Flashcards
If a reaction takes place by SN1, is the mixture optically active?
No. Since the carbocation intermediate is planar, the nucleophile can “attack” either side of the molecule, meaning both enantiomers are produced in equal measure, thus a racemic mixture is formed which isn’t optically active
If a reaction takes place by SN2, is the product optically active?
Yes! Since the nucleophile can only attack the molecule from one side to form the transition state, only one enantiomer is formed so the plane of polarised light is rotated
Conditions and product for reduction of carbonyls
-LiAlH4 in dry ether
-forms an alcohol
-reducing reagent represented as [H]
How is an oxidising agent represented
[O]
What is Tollens reagent and what does it show
-Ag+ complex
-when an aldehyde is present, it undergoes redox with it to be reduced to Ag, forming a silver mirror out of colourless solution
-this is a test for aldehydes only, since ketones can’t be oxidised
What is Fehlings solution and what does it show
-Cu2+ complex
-when an aldehyde is present, it undergoes redox with it by being reduced to Cu+ forming a red precipitate out of blue solution
-since ketones can’t be oxidised, this acts as a test for aldehydes
-this is the same for Benedict’s solution
What does acidified potassium dichromate test for
-presence of aldehyde (colour change from orange solution to green solution)
-will remain orange for ketones since they can’t be oxidised
Describe the iodofrom/ triiodomethane test (Test for what, positive result, conditions)
-tests for the CH3CO group (thus only working for ethanol and methyl ketones)
-positive result is the formation of a yellow precipitate out of colourless solution with a medicinal smell
-conditions=an alkaline solution of I2 that’s heated before being cooled
Reaction with ethanol looks like:
CH3CHO + 2I2 + 2NaOH-> CHI3 + NaI + H2O + CHO-Na+
Conditions and product of nucleophilic addition of CN to carbonyls
-HCN dissolved in an aqueous, alkaline solution of KCN (HCN in KCN)
-produces a hydroxynitrile
-depending on conditions given, the H+ ion may come from either the HCN or an acidic/aqueous work up
-this is an SN1 mechanism, forming a racemic mixture
What does 2,4-DNPH test for? What is a positive result how can the product of this test be used to determine the exact compound present?
-Test for the carbonyl group (so aldehydes and ketones)
-positive result is the formation of a bright red/orange precipitate out of colourless solution
-To determine the exact compound, take the melting point of the derivative by filtering and recrystallising it, then compare to a data book value to find the exact compound
What are the 3 ways of preparing a carboxylic acid?
-oxidising a primary alcohol (with warm acidified potassium dichromate under reflux)
-oxidising an aldehyde (as above)
-hydrolysis of a nitrile (heat under flux with dilute acid or aqueous alkali—acid hydrolysis will straight up produce an acid but base hydrolysis produces a carboxylate salt that can become an acid by adding dilute acid)
Conditions and product of carboxylic acid reduction
-same as carbonyls
-LiAlH4 in dry ether
-forms a primary alcohol
Conditions and product of carboxylic acid neutralisation
-react with aqueous alkali
-forms a carboxylate salt
Conditions and product of carboxylic acid halogenation
-PCl5 in anhydrous conditions (because both the reagent and the acyl chloride are reactive in water)
-forms an acyl chloride (COCl group)
-since HCl is also formed, you may observe steamy fumes, and the POCl3 formed can be separated by fractional distillation
Conditions and reduction of carboxylic acid esterification
-react with an alcohol
-acid catalyst (usually conc. sulphuric)
-reversible reaction
-forms an ester (COO)
