ketone (COC)

OXIDATION ( + [O] )

—preparation of aldehyde

—preparation of ketone

REDUCTION ( + [H] )

—aldehyde and ketone

NUCLEOPHILIC ADDITION WITH HCN

a. RCOOH + NH4+ (dil HCl — hydrolysis)

b. amine (sodium + ethanol)

TESTING ALDEHYDE AND KETONES

INFRARED SPECTROSCOPY

I need to review more on how to draw triiodomethane and the curly arrow diagrams for nucleophilic addition reaction.

Teaching was clear.

a) Aldehyde

b) Ketone

ALDEHYDE

KETONE

OXIDATION OF 1° and 2º ALCOHOLS

CH3CH2OH + 2[O] —> CH3COOH + H2O

CH3CH(OH)CH2CH3 + [O] —> CH3COCH2CH3 + H2O

REDUCTION OF ALDEHYDE AND KETONE

Aldehyde —> Primary Alcohol

Ketone —> Secondary Alcohol

Reduced by: NaBH4 (warmed aq alkaline), LiAlH4 (in dry ether, rtp)

NUCLEOPHILIC ADDITION 

HYDROLYSIS TO FORM RCOOH

RCN + H+ + H2O —> RCOOH + NH4+

RCN + 4[H] —> RCH2NH2

CHEMICAL TESTS

INFRARED SPECTROSCOPY 

WHAT I NEED TO LEARN MORE
Remembering the wave absorption and the constituents of the chemical test reagents.

TEACHING
Teaching was elaborate and concise.

Aldehyde and ketones can be reduced to primary and secondary alcohol respectively using NaBH4 in a warm and alkaline condition while LiAlH4 is used to reduce carboxylic acid to a primary alcohol.

Nucleophilic addition occurs when aldehyde is mixed with hydrocyanic acid (prepared in situ with NaCN and dilute H2SO4) to create a hydroxynitrile that can be reduced to an amine using sodium and ethanol.

The presence of aldehyde and ketone will be tested using 2,4-DNPH (without heating) and deep orange ppt will be seen. Aldehydes are tested using Tollen's reagent (AgNO3 in excess NH3) to see a silver mirror ppt and using Fehling's solution (alkaline solution with Cu2+ ions) to see a brick red ppt forming from a clear blue one. Triiodomethane reaction is used to test for CH3CO and CH3CH(OH) groups and it will form a yellow ppt.

For the IR spectroscopy, 

- alcohol (broad at 3400, sharp at 3000)

- carboxylic acid (very broad at 3000, sharp at 1750)

- ester (sharp at 3000 and 1750)

I need to practice drawing the 2,4-DNPH and the mechanism of nucleophilic addition more.

2.4-DNPH 

-deep orange precipitate when in contact with aldehydes or ketones

tollens reagent 

-will form silver mirror when heated with aldehyde. 

-agno3 in excess nh3.

-ag+ is a mild oxidising agent, it reduced to ag atoms

fehling solution 

-alkaline cu2+ ions

-colour change from blue to red/orange when warmed with aldehydes

nucleophilic addition with hcn

-kcn reacts with halogenoalkane

-hcn reacts with ketone

reactions to form tri-iodomethane

-yellow ppt

-carbonyl compounds js halogenated then hydrolysed

-alkaline solution of iodine is used to halogenate the carbonyl compound

-the reaction is used to test for presence of ch3co- group.

primary alcohol- aldehyde -> carboxylic acid

secondary alcohol- ketone

tertiary alcohol -❌

i need to learn more about the mechanism of reaction because i am not so fluent in that part. 

the class was overall good as usual, mr gopi discussed the materials before going through some past paper questions and then gave us quizziz after school. he also recorded the lesson which made us easier to revise anytime we want.

We also revised the methods of preparing and reducing ketones. To prepare ketones, a secondary is reacted with an oxidation agent and heated under reflux. Unlike preparing aldehydes, since there will be no further reactions after the ketone is formed, there is no need to heat the reactants gently nor to distill the product immediately after formation. To reduce a ketone to a secondary alcohol, it must also be reacted with a reducing agent.

We also revised carbonyl reactions: to prepare for HCN for its nucleophilic addition with a carbonyl compound, NaCN and H2SO4 are heated in situ. The C=O bond in the carbonyl compound is turned into HO≡CN. Nucleophilic addition involves heterolytic fission; C atoms will have a delta positive charge while O atoms will have a delta negative charge.

We also revised tests for aldehydes; 2,4-DNPH (dinitrophenylhydrazine; can also be used to test for ketones), Tollen's reagent, Fehling's reagent and tri-iodomethane can be used.

A positive result using 2,4-DNPH is shown by the formation of an orange precipitate, which can be purified and crystallised, then used to identify the ketone or aldehyde formed. Due to the reactivity of 2,4-DNPH, heating the reactants is unnecessary. 

A positive result using Tollen's reagent is shown by the formation of a silver mirror. Tollen's reagent consists of AgNO3 in a solution of excess NH3; the Ag+ ion acts as an oxidising agent, oxidising the aldehyde into a carboxylic acid. The Ag+ ions are reduced to Ag atoms, forming a "silver mirror". Heating the reactants is necessary.

A positive result using Fehling's reagent is shown by the formation of a red precipitate. Fehling's reagent consists of Cu2+ ions, which is reduced by the aldehyde into Cu atoms, forming a red precipitate.

A positive result using tri-iodomethane is shown by the formation of a yellow precipitate. This only works with the aldehyde ethanal -  tri-iodomethane tests for the CH3CHO group; if it is present, the alkaline solution of iodine forms a (crystallised) yellow precipitate. Heating is necessary.

We also revised infrared spectroscopy; we were advised to ignore values of 800-1400. Alcohol graphs have a distorted blob-like shape, or a "ghost holding up a peace sign" when rotated. It has peak points at 3400 and 3000. Carboxylic acid graphs take on the shape of a mountain, with a broad area at 3000 and a sharp peak at 1750. Ester graphs have a form reminiscent of icicles in a cave, with two sharp edges at 3000 and 1750 respectively.

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To revise: I still have trouble with everything shown in the form of any type of formulae.

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The class was simple and straightforward; it helped me understand things I found difficult when reading the textbook. I also really like it that we take a quizizz after every class. Although I find the time count intimidating, the quiz itself helps me recall what I learned and reminds me of points I would otherwise have missed.

 

Reduction of Aldehyde and Ketone
Aldehyde —> Primary Alcohol

Ketone —> Secondary Alcohol
Reduced by: 

 

 

Comments!
I feel like I need to focus more on the test for Aldehydes and Ketones as memorizing it can be quite challenging sometimes. 

But other than that, Mr Gopi has cleared all other doubts on this chapter when explaining today. It was yet another useful lesson and I'm glad to have him as my chemistry teacher :D Lastly, as the prelims are like in 10 days, I feel like Mr. Gopi has done an amazing job at covering the topics for Organic Chemistry especially since we're having a race against time! 

Preparation of Aldehyde (CHO Group): 

Primary Alcohol + [O] -> Aldehyde

Aldehyde + [O] -> Carboxylic Acid

Note:

To prevent carboxylic acid from forming, heat them gently, add the oxidising agent drop by drop and distill immediately.

Ketone [CO Group]

Secondary Alcohol + [O] -> Ketone

Conditions: Heat under reflux

KMnO4 + heat = purple to colourless

K2Cr2O7 + heat = Orange to green

We also revised on testing for these carbonyl compounds:

2,4 -DNPH

Tollens’ Reagent

Fehling’s solution

Triiodomethane

Nucleophilic addition

Reaction of nitrile

Hydrolysis

Reduction

Reduction of carbonyl

Infrared Spectroscopy

I need to memorize the part on Infrared , the mechanism of nucleophilic addition, the triiodomethane reaction as well as all the reagents and conditions for all the reactions.

When it ends with CHO it is aldehyde. When it is R1COR2 it is ketone.

Primary alcohol will be oxidised to aldehyde and further oxidised to carboxylic acid. Secondary alcohol will be oxidised to ketone but cannot be oxidised further. Tertiary alcohol cannot be oxidised.

When aldehyde needs to be reduced to primary alcohol or when ketone needs to be reduced to secondary alcohol, reducing agents such as NaBH4