Tiêu đề 11.Alcohols, Phenols and Ethers.pdf ✅

ChemContent | Alcohols, Phenols and Ethers ChemContent 1 Introduction • Alcohols and phenols are compounds formed when a hydrogen atom in a hydrocarbon is replaced by– OH group. • An alcohol contains one or more hydroxyl (OH) group(s) directly attached to carbon atom(s) of an aliphatic system. • A phenol contains –OH group(s) directly attached to carbon atom(s) of an aromatic system (C6H5OH). • The substitution of a hydrogen atom in a hydrocarbon by an alkoxy or aryloxy group (R-O/Ar-O) givesanother class of compounds known as ethers. For example:C2H5-O-C2H5 (Dimethyl ether) Nomenclature In case of cyclic compounds, we use the prefix cyclo if the –OH group is attached to C-1.
ChemContent | Alcohols, Phenols and Ethers ChemContent 2 Phenols: Ethers
ChemContent | Alcohols, Phenols and Ethers ChemContent 3 Structures of Functional Groups Alcohols • For alcohols, the –OH group is linked to carbon by a sigma bond. • The bond is formed by the overlap of sp3 hybridised orbital of carbon with a sp3 hybridised orbital ofoxygen. • In alcohols, the bond angle is slightly less than the tetrahedral angle (109°-28’) due to therepulsion between the unshared electron pairs of oxygen. Phenols • In phenols, the –OH group is linked to carbon by sp2 hybridisation. • The C-O bond length (136 pm) in phenol is slightly less than that in methanol. • This arises due to: ➢ Partial double bond character on account of the conjugation of unshared electron pair of oxygenwith the aromatic ring.
ChemContent | Alcohols, Phenols and Ethers ChemContent 4 ➢ sp2 hybridised carbon to which oxygen is linked. Ethers • In ethers the two bond pairs and two lone pairs of electrons on oxygen form a tetrahedral arrangement. • Due to the repulsive interaction between the two bulky (-R) groups the bond angle is slightlygreater than the tetrahedral angle. • The C-O bond length is almost the same like alcohols. Preparation of Alcohols From Alkenes ➢ Acid catalysed hydration: Alcohols are prepared by treating alkenes with water in the presence of acid as catalyst.