Important Notes For Alcohols Phenols and Ethers

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Alcohol Phenol Ether Notes

Alcohol: The hydrogen of an aliphatic hydrocarbon is substituted by the group -OH (hydroxyl).

Phenol: An aromatic hydrocarbon's hydrogen is substituted by the -OH (hydroxyl) group.

Ethers: A hydrocarbon's hydrogen is substituted by the group -OR/-OAr (Alkoxy or Aryloxy).

This article focuses on the complete alcohol phenol and ether notes. So Students will be able to revise the chapter precisely. Besides studying textbooks students can refer to alcohols, phenols, and ethers notes. 


Classification of Alcohols, Phenols, and Ethers

Alcohols:

1. Alcohols are characterized as monohydric, dihydric, trihydric, and polyhydric depending on whether the alcohol contains one, two, three, or more than three hydroxyl groups present respectively.

2. Further monohydric alcohols are classified into-

  • Compounds with Csp3-OH bond- Hydroxyl group is attached to an alkyl group containing sp3 hybridized carbon atom. It is further classified into primary, secondary, and tertiary alcohols.

  • Allylic Alcohols- hydroxyl group is attached to sp3 hybridized carbon atom adjacent to carbon-carbon double bond.

  • Benzylic Alcohols- Hydroxyl group attached to sp3 hybridized carbon atom adjacent to the aromatic ring.

3. Compounds with Csp2-OH bond- the hydroxyl group attached to sp2 hybridized carbon atom. These alcohols are also known as vinylic alcohols.

Phenols: 

Depending on the number of hydroxyl groups it is further classified into monohydric, dihydric, and polyhydric. 

Ethers: 

There are two types of ethers-

  1. Symmetrical- The same groups are attached to O

  2. Unsymmetrical- Different groups are attached to O

Nomenclature

Alcohols: 

  • Common name -'Alcohol 'associated with the alkyl group name, such as methyl alcohol, ethyl alcohol, etc. 

  • IUPAC-The suffix-'ol 'attached to the alkane name, such as methanol (CH3OH).

Phenol: 

  • The simplest phenol is C6H5OH.

  • The OH group location is denoted by o (ortho), m (meta), p (para), or by cyclic carbon numbers, etc.

Ethers: 

  • Common Name: The term 'ether' follows in alphabetical order the name of the alkyl groups, e.g. Ethyl Methyl ether, ether of diethyl, etc. 

  • IUPAC Name-derivative of hydrocarbon named as alkoxy or aryloxy.  The parent hydrocarbon is considered ad the bulkier group, e.g. Methoxymethane, Methoxybenzene, and so on

Structure: 

Alcohols: 

There is a bond between C and O  sp3 hybridized orbitals. 

  • Bond angle: 108.9 ° is the C-O-H bond angle, i.e. less than tetrahedral (109 °-28 '). It is caused by repulsion between Oxygen electron pairs 

  • Bond length: In Methanol, the C-O bond length is 142 pm.

Phenols: 

There is a bond between C of the aromatic ring and O of sp2 hybridized orbitals. 

  • Bond angle: In Phenol, the C-O-H bond angle is 109° 

  • Bond length: The length of the C-O bond in Phenol is 136 pm. 

Due to the sp2 hybridization of Carbon, it is less compared to Methanol, and conjugation of pi electrons of the aromatic ring gives partial double bond character.

Ethers: 

  • Bond angle: The angle of the C-O-C bond is 111.7 (Methoxymethane). 

  • It is more than tetrahedral because of the repulsion between the two classes of R (bulky) 

  • Bond length: The length of the C-O bond is 141 pm, approximately the same as alcohol

Preparation

Alcohols can be prepared by-

  • Acid-catalyzed hydration of alkenes: According to Markovnikov’s addition, alkene in presence of acid reacts with water to form alcohols.

  • The hydroboration oxidation reaction of alkene: trialkyl borane form as an additional product on reacting diborane with alkenes.

  • Carbonyl compounds: Reduction of aldehydes and ketones: aldehydes and ketones are reduced by the addition of hydrogen in the presence of catalysts such as nickel, platinum, and palladium. Aldehyde gives rise to primary alcohols while ketones give rise to secondary alcohols.

  • Reduction of carboxylic acids and esters: In presence of strong reducing agents, lithium hydrogen hydride carboxylic acids are reduced to primary alcohols.

  • Grignard reagent: The addition of RMgX (Grignard reagent) to aldehyde and ketone give rise to alcohol.

Phenols Can be Prepared by-

  • Haloarenes: NaOH is treated with chlorobenzene to form sodium phenoxide, which is then treated with acid to form phenol.

                                   C6H5Cl + NaOH → C6H5ONa + HCl → C6H5OH

  • Benzene sulphonic acid: Sulphonation of benzene with oleum is the first step. Benzene sulphonic acid thus formed is heated to form sodium phenoxide with molten NaOH and then acidified from phenol.

  • Diazonium salt: Aniline (C6H5NH2): It reacts with NaNO2 + HCl forms Benzene diazonium chloride (C6H5N2Cl), which on hydrolysis give phenol.

  •  Cumene (isopropylbenzene): It is oxidized and then treated with dilute acid to form phenol. Acetone in the reaction is a by-product.

Ethers Can be Prepared by

  • Dehydration of alcohols: The nucleophilic bimolecular reaction produces ether when primary alcohols are treated with protic acids (H2SO4, H3PO4). This reaction depends on the conditions, while alkene is a major product at 443 K and ether is a major product at 413 K. Elimination reaction competes with SN1 when alcohol is 2 ° or 3 °, resulting in alkene as the main product.

  • Williamson synthesis 

Physical Properties:

Alcohol:

Boiling point: With the increase in the number of carbon atoms, Van der Waal forces, thus increase the boiling point of alcohols.

Solubility: Alcohols are soluble in water as they form hydrogen bonds with water molecules.

Phenol:

Boiling point: Due to intermolecular hydrogen bonding, the boiling point of phenol is more as compared with other compounds such as arenes, ethers, haloarenes, etc.

Solubility: Solubility is due to intermolecular hydrogen bonding with water. It decreases with an increase in the hydrophobic part.

Ethers: 

The boiling point is comparatively less than that of alcohols due to intermolecular hydrogen bonding in alcohols.

Owing to the formation of a hydrogen bond with water and O of ether, ether miscibility is equivalent to alcohol and more than alkane of the same molecular mass.


Acidity and Basicity:

Alcohols: 

  • Bronsted acids can donate electrons to the Bronsted base.

  • Acidity is caused by the O-H bond's polarity. The acidity is reduced by the electron releasing alkyl groups, so the alcohol acidity order is: 1o > 2o > 3o degrees 

  • Water is a stronger donor of protons or more potent acid than alcohols 

  • Because of unshared electron pairs on oxygen, they also serve as a proton acceptor or Bronsted base

Phenol: 

  • Benzene ring with alcohol group acts as an electron-withdrawing group.  Oxygen electron pairs are paired with the double bond of the benzene ring, which makes OH oxygen positive. 

  • Phenols are acids that are stronger than water and alcohol. 

  • The more stable phenoxide ion and the more polar OH bond may clarify this. 

  • In the substituted phenols, the electron-withdrawing group (-NO2) makes it more acidic and the electron-donating groups (alkyl) reduce the acidity. 

  • Order of acidity:Nitrophenol > Phenol > Cresol > Ethanol

Ethers: Ethers are less acidic than aldehydes and ketones but more acidic than hydrocarbons


Chemical Reactions-

Alcohols: 

  • Reactions in which alcohol (O-H bond cleavage) reacts as a Nucleophile: Reaction of alcohol with metal to form alkoxide.On the reaction of alcohols with carboxylic acids, acetic anhydride, and acid chloride to form esters.

  • Reactions in which there is C-O bond cleavage: Alcohol reacts with HX to form alkyl halide.

  • Undergo oxidation to form aldehyde and ketone.

  • On heating with Cu at 573K, alcohols undergo dehydrogenation

Phenol: 

  • Reactions in which phenol (O-H bond cleavage) reacts as a Nucleophile: The reaction of phenol with NaOH to form sodium phenoxide.On the reaction of phenols with carboxylic acids, acetic anhydride, and acid chloride to form esters.

  • Reactions in which there is C-O bond cleavage:

                           C6H5OH + Zn → C6H6 + ZnO

  •  Electrophilic substitution reaction

  1. Nitration

  2. Halogenation

  3. Koble reaction

  4. Reimer-Tiemann Reaction

  5. Oxidation

Ethers: 

  • Absence of O-H bond in ethers

  • Reactions with CO bond cleavage

  • Electrophilic Substitution reaction

  • Friedel Crafts Reaction

Conclusion 

When a saturated carbon atom is bound to a hydroxyl (-OH) group, alcohol is formed. Phenol is formed when the -OH group replaces a hydrogen atom in a benzene molecule. When an oxygen atom is linked to two alkyl or aryl groups, ether is formed.

FAQ (Frequently Asked Questions)

1. Which is More Acidic: Phenol or Ether? 

Answer: Phenol is more acidic than alcohol, and with sodium hydroxide solution, H+ can be extracted. Compared to carboxylic acids, it is less acidic. Hence, phenol is more acidic than ether.


2.Why isn't Phenol an Alcohol? 

Answer: An-OH bonded to an unsaturated sp2 carbon consists of a phenol. Therefore,  phenol is not considered an alcohol.

3. Which Test Indicates That Phenol is Present? 

Answer: To assess the presence of phenols in a given sample or compound, the ferric chloride test is used (for instance natural phenols in a plant extract). Positive results are also given by enols, hydroxamic acids, oximes, and sulfinic acids.

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