Alcohols & Phenol, Nomenclature, Classification & Properties, Study notes of Organic Chemistry

Download Alcohols & Phenol, Nomenclature, Classification & Properties and more Study notes Organic Chemistry in PDF only on Docsity! ALCOHOLS & PHENOL: NOMENCLATURE, CLASSIFICATION & PROPERTIES BS-Chemistry (Semester-II) By Dr. Aliya Ibrar Dated: 21-05-2021 a IUPAC RULES 1. Select the longest continuous chain of carbon atoms containing the hydroxyl group. 2. Number the carbon atoms in this chain so that the one bonded to the —OH group has the lowest possible number. 3. Form the parent alcohol name by replacing the final —e of the corresponding alkane name by —o/. When isomers are possible, locate the position of the -OH by placing the number (hyphenated) of the carbon atom to which the —OH is bonded immediately before the parent alcohol name. 4. Name each alkyl branch chain (or other group) and designate its position by number. This is the longest continuous chain that contains an hydroxyl group. Select this chain as the parent compound. OH H3Cv | \SCH—CH—CH; H3C 4 OH H3C_ 3 \CH—CH—CH3 HsC 2 1 a This end of the chain is closest to the OH. Begin numbering here. 5|[4] [3] OF H3C —-CH2—CH—CH-—CH3 2 CH3/2| |1 \ This end of the chain is closest to the OH. Begin numbering here.  sj[4] BT H3C—CH»—CH—CH-Ch3 Hg ~ CHa CH= CH= CHs cH, 1 JPAC name: 3-methyl-2-pentanol New IUPAC name: 3-methylpentan-2-ol NOMENCLATURE OF CYCLIC ALCOHOLS = Using the prefix cyclo- = The hydroxyl group is assumed to be on C1. H : 20H HO CH,CH, 1 7 JX, Br IUPAC name: _ trans-2-bromocyclohexanol 1-ethylcyclopropanol new IUPAC name: trans-2-bromocyclohexan-1-ol 1-ethylcyclopropan-1-ol = Some consideration: - OH functional group is named as a hydroxy substituent when it appears on a structure with a higher priority functional group such as acids, esters, aldehydes and ketones. - Examples: OH Oo OH mC ill CH,—CH—CH,— C—OH No 3-hydroxybutanoic acid 2-hydroxycyclohexanone  MAIN GROUPS decreasing priority Acids Esters Aldehydes Ketones Alcohols Amines Alkenes Alkynes Alkanes Ethers Halides —E th NOMENCLATURE OF DIOLS = Alcohols with two -OH groups ——— diols or lycols. = Naming of diols is like other alcohols except that the suffix dio! is used and two numbers are needed to tell where the two hydroxyl groups are located. OH > OH | <T. ; “OH 1 CH,;—CH—CH,— OH a IUPAC name propane-1,2-diol trans-cyclopentane-1,2-diol eee COMMON NAMES = Derived from the common name of the a/ky/ group and the word a/cohol. = For examples: cH, H3C-C-OH CH; CH;CH,OH IUPAC name: 2-methyl-2-propanol IUPAC name: ethanol Common name: tert-butyl alcohol Common name: ethyl alcohol CH,CHCH, I CH,;0H OH IUPAC name: 2-propanol IUPAC name: methanol Common name: isopropyl alcohol Common name:methy! alcohol I 7 EEE t—te a CLASSIFICATION OF ALCOHOLS * Se CLASSIFICATION = According to the type of carbinol carbon atom (C bonded to the — OH group). —t—on = Classes: i) Primary alcohol - -OH group attached to a primary carbon atom - one alkyl group attached ii) Secondary alcohol - -OH group attached to a secondary carbon atom - two alkyl group attached iii) Tertiary alcohol - -OH group attached to a tertiary carbon atom - three alkyl group attached a SS a PHYSICAL PROPERTIES OF ALCOHOLS a PHYSICAL PROPERTIES m PHYSICAL STATES OF ALCOHOLS - aliphatic alcohols and lower aromatic alcohols —— liquids at room temperature. - highly branched alcohols and alcohols with twelve or more carbon atoms —— solids. ESF = BOILING POINTS i) Boiling points of alcohols are higher > alkanes and chloroalkanes of similar relative molecular mass. - For example: C,H,OH CH,CH,CH, CH,CI Relative molecular mass: 46 44 50.5 Boiling point: 42 C -24C - Reason: * intermolecular hydrogen bonds Re 5. 6+ AT. 6- co --- H. R orto tigy Ar H hydrogen bonding ny drogen ie ee ACIDITY OF ALCOHOLS AND PHENOLS = Alcohol ———~> weakly acidic. = In aqueous solution, alcohol will donated its proton to water molecule to give an alkoxide ion (R-O)). R-OH + H,O R-O- + H,0* K, = ~ 10° to 10°78 alkoxide ion Example = The acid-dissociation constant, Ka, of an alcohol is defined by the equilibrium R-OH + H,0 ~@ R-O° + H,0* * More smaller the pK, F value, the alcohol is Ka = [H,0*] [RO] pK, = - log (K,) more acidic [ROH] a ACIDITY OF PHENOLS = Phenol is a stronger acid than alcohols and water. R-OH + H,O = R-O°-+H,0* K,=~ 10" to 10°8 alcohol alkoxide ion ( )-0H oO) ——— (po a H,0* K, = 1.2 x 10°79 phenol phenoxide ion H,O0+ HO =— HO + H,0* K=16x 10" hydroxide ion = Phenol is more acidic than alcohols by considering the resonance effect. i) The alkoxide ion (RO) - the negative charge is confined to the oxygen and is not spread over the alkyl group. - this makes the RO- ion less stable and more susceptible to attack by positive ions such as H* ions. ee IMPORTANT OF ALCOHOL = Ethanol - solvent for varnishes, perfumes and flavorings, medium for chemical reactions and in recrystallization. Also is an important raw material for synthesis. = Medically, ethanol is classified as a hypnotic (sleep producer), it is less toxic than other alcohol. = Ethanol is prepared both by hydration of ethylene and by fermentation of sugars. It is the alcohol of alcoholic beverages. i Cl CH, =CH, + H,O ————— CH,CH,OH C,H,,0, emma > 2CH,CH,OH + 2CO,