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Organic Compounds containing Oxygen is an important topic in JEE Main Chemistry. It occupies a very important position under the broader heading of General Organic Chemistry. Around 1-2 questions are asked from Organic Compounds containing Oxygen which carry a total of around 4 marks. Therefore, the total weightage of this chapter is around 1-2% in JEE Main. If you memorize the theory from this chapter well, the questions can be quite easy to score. Some of the concepts tested under Organic Compounds containing Oxygen are - Alcohols, Ethers, and Cannizzaro Reaction. Read Complete JEE Main Syllabus
Read the article given below for study notes on Organic Compounds containing Oxygen to ace JEE Main scheduled to be conducted
Must Read Study Notes
Alcohols can react as nucleophiles and electrophiles.
Reaction with metals - Alcohols and phenols react with active metals such as Na, K, and Al to provide the corresponding alkoxides or phenoxides with the production of hydrogen.
2R-OH + 2Na → 2R-O-Na + H2
Alcohols display only the reactions that involve the cleavage of C-O bond. Phenols display this kind of reaction solely with zinc.
Reaction with hydrogen halides
Alcohols, when treated with hydrogen halides, make alkyl halides.
ROH + HX → R-X + H2O
Reaction with Phosphorus trihalides
Alcohols become converted into alkyl bromides when treated with PBr3.
3R-OH + PBr3 → 3R-Br + H3PO3
Alcohols go through dehydration to create alkenes when conc. H2SO4 or H3PO3 is present or catalysts like anhydrous zinc chloride or alumina are there.
Primary alcohol goes through dehydration when heated with conc. H2SO4 at 443K.
Secondary and tertiary alcohols go through dehydration under conditions which are
Therefore, the ease with which the dehydration of alcohols takes place follows the order given below -
Tertiary > Secondary > Primary
The oxidation of alcohols leads to the formation of a carbon-oxygen double bond with the cleavage of an O-H and C-H bonds. This reaction is called the dehydrogenation reaction because it goes through a loss of dihydrogen from a molecule of alcohol.
The usage of strong oxidising agents such as acidified KMnO4 is done to form carboxylic acids directly from alcohols. CrO3 in anhydrous medium is utilized to form aldehydes. CrO3 is used for the oxidation of secondary alcohols to ketones.
Pyridinium chlorochromate (PCC), which is a complex of chromium trioxide with pyridine, and HCl is a better oxidizing agent for the oxidation of primary alcohols to aldehydes with a good output.
Phenols display electrophilic substitution reactions.
The –OH group begins activation of the benzene ring in the direction of electrophilic substitution. It even directs the incoming group to ortho and para positions in the ring when these positions turn electron rich owing to the resonance effect which is caused by the –OH group.
Phenol > H2O > Primary alcohol > Secondary alcohol > Tertiary alcohol
The acidic character of alcohols exists due to the polar nature of the O–H bond.
Distinguishing among a few important organic compounds -
Phenol and alcohol
Phenol when reacted with neutral FeCl3 provides a purple colour while alcohols do not provide a purple colour.
6C6H5OH + Fe3+ → [Fe(OC6H5)6]3− + 6H+
Primary, secondary and tertiary alcohols
Lucas reagent test:
When it is a primary alcohol, no turbidity is seen at room temperature. Turbidity becomes visible only on heating.
When it is a secondary alcohol, the turbidity is seen in 5 minutes.
When it is a tertiary alcohol, the turbidity shows up immediately.
Methanol and ethanol
Ethanol if reacted with I2 and NaOH or NaOI provides a yellow ppt. of iodoform due to the existence of the CH3–CH (OH)− group.
C2H5OH + 4I2+ 6NaOH → CHI3 + 5NaI + 5H2O + HCOONa
CH3OH + I2+ NaOH → No yellow ppt.
The cleavage of C–O bond in ethers
Because ethers are the least reactive among all the functional groups, the cleavage of C-O bond in ethers occurs when there is an excess of hydrogen halides.
The cleavage of ethers that have two distinct alkyl groups also occurs in a similar manner.
Given below is the order of reactivity of hydrogen halides -
HI > HBr > HCl
Electrophilic substitution reaction in aromatic ethers
Reactions of Aldehydes and Ketones
In nucleophilic addition reactions, aldehydes are typically more reactive than ketones because of steric and electronic reasons or the inductive effect.
Nucleophilic addition reactions of aldehydes and ketones
The addition of hydrogen cyanide (HCN) to create cyanohydrins
The Addition of sodium hydrogen sulphite (NaHSO3) to create bisulfite addition compound
The addition of Grignard reagent (RMgX) to make alcohol
The addition of alcohol
i. When monohydric alcohol is added in the presence of dry HCl, aldehydes create hemiacetal and acetal.Ketones do not react with monohydric alcohols. Instead, they react with ethylene glycol under such conditions to create cyclic products which are called ethylene glycol ketals.
The addition of ammonia and its derivatives
a. The reduction to alcohols
When catalytic hydrogenation takes place in the presence of Ni, Pt or Pd with the use of lithium aluminium hydride ( ) or sodium borohydride ( ), aldehydes and ketones respectively create primary and secondary alcohols.
b.Reduction to hydrocarbons
i. Clemmensen reduction: The carbonyl group of aldehydes and ketones gets reduced to the CH2 group when treated with zinc amalgam and concentrated hydrochloric acid.
ii. Wolff–Kishner reduction: The carbonyl group of aldehydes and ketones gets reduced to the CH2 group when treated with hydrazine following which heating with sodium or potassium hydroxide in a high boiling solvent like ethylene glycol takes place.
Aldehydes get oxidised to acids when mild oxidising agents like HNO3, K2Cr2O7, or KMnO4 are present.
Ketones are typically oxidised in severe conditions, that is, with strong oxidising agents like conc. HNO3, KMnO4/H2SO4 and K2Cr2O7/H2SO4 at a raised temperature.
Note: Cleavage happens in a way that the keto group stays with the smaller alkyl group in unsymmetrical ketones. This is called the Popoff’s rule.
Haloform reaction: Aldehydes and ketones with a minimum of one methyl group connect to the carbonyl carbon atom, that is, methyl ketones get oxidised by sodium hypohalite to sodium salts of respective carboxylic acids having one carbon atom lower than that of the carbonyl compound. The methyl group turns to haloform.
Aldol condensation: Aldehydes and ketones with a minimum of one α-hydrogen go through self-condensation when dilute alkali as a catalyst is present to create α-hydroxy aldehydes (aldol) or α-hydroxy ketones (ketol), respectively.
Cross aldol condensation: Aldol condensation among two distinct aldehydes and ketones is known as aldol condensation. When both of them possess α-hydrogen atoms, a mixture of four products is formed.
Aldehydes that do not contain an α-hydrogen atom go through self-oxidation and reduction (disproportionation) reaction when treated with concentrated alkali to create alcohol and salt of acid.
Tollen’s test: If an aldehyde undergoes heating with the Tollen’s reagent, it makes a silver mirror. Tollen’s reagent is an ammoniacal solution of AgNO3.
A silver mirror is not created by ketones.
Fehling’s test: If an aldehyde undergoes heating with the Fehling’s reagent, it creates a reddish-brown precipitate of cuprous oxide.
Fehling’s reagent: Fehling solution A (aqueous solution of CuSO4) + Fehling solution B (this is the alkaline solution of sodium potassium tartrate)
Ketones do not make a reddish-brown precipitate of cuprous oxide.
Reactions that involve the cleavage of C–OH bond: Carboxylic acids when heated with mineral acids like H2SO4 or with P2O5 create respective anhydrides.
Esterification: Carboxylic acids get esterified with alcohols when a mineral acid like concentrated H2SO4 or HCl gas as a catalyst is present.
Carboxylic acids react with PCl5, PCl3 and SOCl2 to make acyl chlorides.
Reaction with ammonia (NH3): Carboxylic acids when reacted with ammonia give ammonium salt. When heated further at high temperature, it creates amides.
Reactions that involve the COOH group
Reduction: Carboxylic acids become reduced to alcohols when LiAlH4 or B2H6 are present.
Decarboxylation: Sodium or potassium salts of carboxylic acids when heated with soda lime (NaOH + CaO in ratio of 3:1) provide hydrocarbons that consist of one carbon lower than the parent acid.
Reactions involving substitution reaction in hydrocarbon part
Hell–Volhard–Zelinsky reaction: Carboxylic acids that have an α-hydrogen get halogenated at the α-position when treated with chlorine or bromine. This happens in the presence of a small quantity of red phosphorus to produce α-halo carboxylic acids).
Ring substitution in aromatic acids: Aromatic carboxylic acids go through electrophilic substitution reactions. The carboxyl group in benzoic acid is electron-withdrawing group and meta directing.
From Alkenes: Alkenes when reacted with water when acid is present forms alcohol. When unsymmetrical alkenes are present, the alcohol is created through MArkovnikov's rule.
From carbonyl compounds: LiAlH4 is a very powerful reducing agent.
From haloarenes: Chlorobenzene is utilized to react with NaOH at a high temperature and pressure. Sodium phenoxide is created. This is then acidified to give phenol.
From cumene: Cumene gets oxidised when air is present and gets converted to cumene hydroperoxide. This hydroperoxide when treated with dilute acid gives phenol.
Dehydration of alcohols: Alcohol gets dehydrated to ether when an acid such as H2SO4 at 413K is present.
Williamson synthesis: Phenol when treated with sodium hydroxide produces sodium phenoxide. This phenoxide then turns to ether.
Dehydration: Alcohol gets dehydrated when an acid is present to give alkene at 443K.
Acylation of alcohols: Alcohol gets treated with an acyl group when pyridine is present and gives -
Electrophilic aromatic substitution: Phenol on being treated with dilute HNO3 at a low temperature gives ortho and para nitrophenols.
Kolbe's reaction: Phenol gets treated with sodium hydroxide and gives phenoxide. This phenoxide when treated with carbon dioxide gives hydroxybenzoic acid.
Reimer-Tiemann reaction: Phenol gets treated with chloroform when sodium hydroxide is present. Then, a CHO group becomes connected at the ortho position of phenol and gives salicylaldehyde.
Cleavage of C-O bond in ethers: Ether gets treated with hydrogen iodide and gives the alcohol and tertiary halide.
Friedel-Crafts reaction: Anisole gets treated with alkyl and acyl groups and they become attached at the ortho and para positions. This reaction happens when a catalyst called anhydrous aluminum chloride is present.
Nitration: Anisole gets treated with a mixture of concentrated sulphuric acid and nitric acid. It gives a mixture of ortho and para nitroanisole.
From acyl Chloride: Acyl chloride is treated with hydrogen when palladium-barium sulphate as a catalyst is present. This reaction is called the 'Rosenmund reduction'.
Gatterman-Koch reaction: Benzene gets treated with carbon monoxide and hydrogen chloride when anhydrous aluminum chloride is present. The product it gives is benzaldehyde. This reaction is called the Gatterman-Koch reaction.
From Nitriles: The nitrile gets treated with the Grignard reagent and forms a ketone.
Friedel-Crafts Acylation reaction: Benzene or substituted benzene gets treated with an acyl chloride when anhydrous aluminum chloride is present and forms a ketone. This reaction is called the Friedel-Crafts Acylation reaction.
From primary alcohols: Primary alcohols get oxidised to respective carboxylic acids when some oxidising agents like alkaline KMnO4 are present.
From Esters: The acidic hydrolysis of esters provides respective carboxylic acids.
Clemenson’s Reduction: Aldehydes or ketones get treated with zinc amalgam and concentrated hydrochloric acid. The carbonyl group of aldehydes and ketones reduces to CH2. This reaction is called the Clemenson’s Reduction.
Intermolecular Aldol Condensation: Two distinct aldehyde compounds react with each other when sodium hydroxide is present and different products are produced.
Intramolecular Aldol Condensation: The compound reacts by and in itself when a base is present.
Intermolecular Cannizzaro reaction: Two aldehyde compounds react with one another when sodium hydroxide is present and give alcohol and a carboxylic acid salt.
Benzoin Condensation: This is considered to be a condensation reaction. It happens among two aromatic aldehydes and gives an acyloin.
Reduction: Carboxylic acids get reduced to amides when ammonia is present.
Decarboxylation: Carboxylic acids get reduced to respective alcohols when LiAlH4 is present. These alcohols get reduced further to hydrocarbons when their sodium salts get heated with soda lime.
Electrophilic Substitution: Aromatic carboxylic acids go through an electrophilic substitution reaction. Here, the carboxyl group behaves like a meta directing group.
Questions from this chapter are theory-based. It is very essential for you to understand and memorize the concepts and reactions.
Practice writing down the reactions repeatedly while preparing for this chapter.
Attempt questions from within the chapter and those given after the chapter for thorough recall of mechanisms.
Ensure that you study first from NCERT books to develop a strong foundational base of this chapter before using any additional reference books.
For MCQs that require you to identify products or reactants, visualize the entire process before choosing an answer.
|Week 1 (June 7 to 14)||Physical Chemistry bears the most weightage in JEE Main Chemistry. High-weightage chapters from this area such as Electrochemistry, Atomic Structure, and Equilibrium to be studied in the beginning. Then, study less important chapters like Surface Chemistry and Solid State. Pick two chapters each day and study all the essential concepts and reactions.|
|Week 2 (June 14 to 20, 2020)||Study Organic Chemistry during this week. Allocate more time to chapters with high weightage such as Aromatic Compounds, Alcohol, Alkyl Halides, and Ether. Then, study chapters with lower weightage such as Biomolecules and Carbonyl Compounds.|
|Week 3 (June 21 to 27, 2020)||Study Inorganic Chemistry for this week. Start by studying chapters with the highest weightage like p Block, s Block, and Chemical Bonding. Move on to study less important chapters such as Metallurgy and Qualitative Analysis.|
|Week 4 (June 28 to -July 4, 2020)||Brush through your study notes, important concepts, and reactions. Answer previous year’s papers for enhanced practice. Pick out questions from the Chemistry section and attempt them as quickly as you can, preferably within 45 minutes to 1 hour.|
|Week 5 (July 5 to 11, 2020)||Attempt mock tests every day of this week.|
|Week 6 (July 12 to 17, 2020)||Revise important concepts and reactions from all the chapters.|
|JEE Main Exam Week (July 18 to 23, 2020)||Read the analysis of ongoing JEE Main papers.|