1 2. 3. Preparation from carbonyl compounds: Tertiary alcohols cannot be prepared by this method. On REDUCTION : Aldehydes → 10 alcohols ketones → 20 alcohols. List of reducing agents: 1. Hydrogen and metal like Pd, Ni , Pt - (Catalytic hydrogenation) 2. Sodium borohydride (NaBH4) 3. Lithium aluminium hydride (LiAlH4). NOTE: LiAlH4 is an expensive reagent, and therefore, used for preparing special chemicals only. So, ethanal → ethanol Propanal → Propanol Butanal → butanol 2. : Why NaBH4 is not used ? Commercially, carboxylic ( RCOOH) 4. Reagent on aldehydes or ketones . Preparation of primary alcohol : formaldehyde Preparation of secondary and tertiary alcohol : From Grignard Reagent: So, With Grignard Reagent : Methanal → 1O Alcohol, Other Aldehydes → 20 Alcohol, Ketones → 30 Alcohols Home assignment : ncert intext example 11.2 intext question 11.4 , 11.5 Q11.20 How are the following conversions carried out? (i) Propene → Propan-2-ol. (ii) Benzyl chloride → Benzyl alcohol. (iii) Ethyl magnesium chloride → Propan-1-ol. (iv) Methyl magnesium bromide → 2-Methylpropan-2-ol. Ncert q 11.10 1. From haloarenes 2. 3. Preparation of phenol from diazonium salt Ncert q 11.9 • In alcohols, the oxygen of the –OH group is attached to carbon by a sigma ( σ ) bond formed by the overlap of a sp3 hybridised orbital of carbon with a sp3 hybridised orbital of oxygen. The bond angle in alcohols is slightly less than the tetrahedral angle (109°-28′). REASON: It is due to the repulsion between the unshared electron pairs of oxygen. In phenols, the –OH group is attached to sp2 hybridised carbon of an aromatic ring. The carbon– oxygen bond length (136 pm) in phenol is slightly less than that in methanol. REASON : This is due to (i) partial double bond character on account of the conjugation of unshared electron pair of oxygen with the aromatic ring (ii) sp2 hybridised state of carbon to which oxygen is attached. (more electronegative and shorter and stronger bond.) • In ethers, the four electron pairs, i.e., the two bond pairs and two lone pairs of electrons on oxygen are arranged approximately in a tetrahedral arrangement. The bond angle is slightly greater than the tetrahedral angle((109°-28′). ) REASON: due to the repulsive interaction between the two bulky (–R) groups. The C–O bond length (141 pm) is almost the same as in alcohols.
