Organic Chemistry Lecture 1 PDF

Organic chemistry lecture 1 1/6 Alcohols and phenols Alcohols and phenols are compounds characterized by presence of OH group...

Organic chemistry lecture 1 1/6 Alcohols and phenols Alcohols and phenols are compounds characterized by presence of OH group. If OH group is attached to alkyl group it is called alcohol but if the OH group is attached to aromatic system we called it phenol R OH alcohol OH phenol Ar OH Ar = aryl Classification and Naming of Alcohols and Phenols O H H Replace one Replace both hydrogen hydrogen w ith an alkyl w ith an aryl w ith tw o alkyl w ith one alkyl w ith tw o aryl group group groups and one aryl groups groups ROH ArOH ROR ArOAr ArOR Ethers 1- Primary alcohol CH3CH2OH CH3 2- Secondary alcohol CH3 CH OH 3- Tertiary alcohol Application to Biochemistry Blood sugar (glucose) contains five alcohol groups. Using the structure of glucose. 1  Organic chemistry lecture 1 2/6 Lower alcohols have common names CH3CH2OH , CH3CH2CH2CH2OH , CH3 CH CH2 CH3 Ethyl alcohol n. butyl alcohol OH secondary butyl alcohol Allyl alcohol Alcohol containing more than five carbons are best named by the IUPAC rules. 1- The longest continuous chain of carbon atoms that contains the hydroxyl group is taken as the parent chain. 2- The parent name is obtained by substitution of the ending-ol for the ending –e of the corresponding alkane. 3- The chain is numbered to give the lowest number to the carbon bonded to the hydroxyl group. 4- The suffix-ol is used for one hydroxyl group ; diol for two ;-triol , for three , and so forth. For higher alcohols we use IUPAC system. CH3 CH2CH3, CH3 CH CH CH CH3 OH 3-ethyl-4-methyl-2-pentanol 3-bromo-5-chloro-4-phenyl-2-hexanol 2-chloro-6-methyl-3-nitrophenol Physical properties Alcohol and Ether are isomers of each other of the same molecular formula e.g C4H10O CH3 CH2 O CH2 CH3 CH3 CH2 CH2 CH2 OH Important note: The boiling point of alcohol and phenol is higher than the ethers due to presence of hydrogen bonding R O H Hydrogen bond R O H R O H R O H 2  Organic chemistry lecture 1 3/6 Solubility : Alcohol and phenol are soluble in water due to forming of hydrogen bonding with water , but Ethers are insoluble in water. Preparation of alcohols 1-Hydration of alkenes : The acid-catalyzed addition of water to an alkene forms an alcohol as a product.This reaction , adds water to the double bond according to the markownikoff rule. H+ CH3CH CH2 + HOH CH3 CH CH 3 OH the addition follows markonikof rule 2- Reduction of carbonyl compounds : alcohol can be prepared by adding hydrogen to the carbon-oxgen double bond of certain carbonyl compounds. The reaction is called the reduction of carbonyl compounds.The reductions of aldehydes and ketones are example of these reactions: a. By use of H2 catalyst C O C OH H H H H R C O Pt R C OH catalyst H H aldehyde primary alcohol R R R C O Pt R C OH catalyst H H ketone secondary alcohol b- Another reagent that reduces carbonyl compounds is Lithium aluminum hydride ( LiAlH4 ): H H H 4 H2O 4 R C O + LiAlH4 R C O AlLi R C OH + LiOH + Al(OH)3 hydrolysis H H 4 aldehyde Lithium aluminum alkoxide (note) This reaction happen also with ketone only changing H to R. 3  Organic chemistry lecture 1 4/6 Reaction of alcohols a. Dehydration : alcohol reacts with concentrated sulfuric acid (H2SO4) to eliminate a molecule of water to form an alkene , as shown by the following equation (reaction is reverse ) H H2SO4 R C CH2OH RCH CH2 + H2O alkene H If we use small amount of H2SO4 the reaction will shift to the left leading the formation of alcohol. but if we used large amount of H2SO4 the reaction will shift to the right lead to the formation of alkene , ease of dehydration of alcohol will be in this order 3o alcohol > 2o alcohol > 1o alcohol CH3 CH3 H2SO4 CH3 C OH o CH3 C CH2 + H2O 25 C CH3 t. butanol isobutene CH3 H2SO4 CH3 CH OH o CH3 CH CH2 + H2O 100 C isopropanol H2SO4 CH3 CH2 OH o CH2 CH2 + H2O 150 C Oxidation The product of oxidation of alcohols depend on the structure of the alcohol. primary alcohol are first oxidized to aldehydes, which are further oxidized to carboxylic acid. Secondary alcohols form ketones on oxidation , and tertiary alcohol are not easily oxidized. One of H these H O O O O hydrogen R C O R C R C H OH is remove H Primary alcohol aldehyde carboxylic acid 4  Organic chemistry lecture 1 5/6 H H O R R C O C O R R Secondary alcohol ketone R H O R C O no reaction R Tertiary alcohol Ester formation Alcohols reacts with carboxylic acids in the presence of a strong acid catalyst to form a class of compounds called esters. The general equation for this reaction is the following O + O H ROH + RC RC + HOH OH OR alcohol carboxylic acid ester water Oxidation of alcohol in living system These reactions are important in living system catalyzed by enzymes called (dehydrogenases) For example: oxidation of malate malate oxaloacetate - - CO2 CO2 dehydrogenase H C OH C O - - CH2CO2 CH2CO2 malate oxaloacetate sec. alcohol Another example: the reaction is known to require the presence of nicotinamide , a derivative of pyridine. Because the nicotinamide is linked to the enzyme , the enzyme is called pyridine linked – dehydrogenase 5  Organic chemistry lecture 1 6/6 These two hydrogens are removed H O O - H H H C CO2 C - NH2 NH2 O2C C OH + C O + + H2 - - CH2CO2 N+ CH2CO2 N R R L-malate enzyme-bond oxaloacetate reduced nicotinamide enzyme-bound nicotinamide This reaction is very stereospecific. The L-malate is only oxidized by this enzyme but not D-malate which is the mirror image of L-malate. 6