Lecture Note Alkanes - Hydrocarbon Chapter 2.0 Introduction...

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Unformatted text preview: Hydrocarbon Chapter 2.0 Introduction Classification of Hydrocarbon Hydrocarbon Hydrocarbon Aromatic Alkynes Aliphatic Alkanes Alkenes Cycloalkanes Cycloalkenes Saturated Unsaturated Introduction to Hydrocarbons Hydrocarbons Hydrocarbons Aliphatic Aliphatic Aromatic Aromatic Hydrocarbons • simplest organic compounds • contain only carbon and hydrogen Hydrocarbons Hydrocarbons • Aliphatic Aliphatic Alkanes are hydrocarbons in which all of the bonds are single bonds. H H H C H C H H Alkanes Alkanes Hydrocarbons Hydrocarbons • Alkanes whose carbon atoms are joined in rings are called cycloalkanes. They have the general formula CnH2n where n = 3,4,… Aliphatic Aliphatic CycloAlkanes CycloAlkanes Hydrocarbons Hydrocarbons • Aliphatic Aliphatic Alkenes are hydrocarbons that contain a carboncarbon double bond. H H C H C H Alkenes Alkenes Hydrocarbons Hydrocarbons • Aliphatic Aliphatic Alkynes are hydrocarbons that contain a carboncarbon triple bond. Alkynes Alkynes HC CH Hydrocarbons Hydrocarbons • The most common aromatic hydrocarbons are those that contain a H benzene ring. H H H H H Aromatic Aromatic Hydrocarbon – Alkanes Chapter 2.1 Alkanes Alkanes nomenclature system Structural isomers Cycloalkanes Sources of alkanes and cycloalkanes Synthesis of alkanes Reaction of alkanes Alkanes Simplest members of hydrocarbon family • Contain only hydrogen and carbon • Only have single bonds • Saturated compound All members have general formula of CnH2n + 2 Twice as many hydrogen as carbon + 2 Alkane Nomenclature 24.2 Alkyl Groups Alkyl group is a group which is derived from Alkyl derived unbranchedunbranched removing unbranched-chain alkanes by removing 1 H atom from from the end C atom General General formula : CnH2n + 1 Represented Represented by “R” symbol suffix suffix : - yl Names of some common alkyl groups Alkane Alkane methane ethane Alkyl methyl ethyl propyl Structure - CH3 - CH2 CH3 H H C H H C H H C H propane H H C H H C H C H 10 H H H C H CH H H isopropyl H C H 20 Alkane Alkane butane H H C H H C H H C H C H Alkyl H Structure H C H H C H H C H H C H C H H C H H butyl 10 H H C H H H 20 secsec-butyl H C H H CH3 H C H C H isobutyl H H C H CH3 H C H H C H 10 H C H 30 H CH 3 H C C H H terttert-butyl H C H Alkane Alkane pentane H H C H H C H H C H H C H H C H 10 Alkyl H H C H Structure H C H H C H H C H H C H pentyl H H H C H H C H C H C H H H C H C H C H H isopentyl H C H CH3 H CH3 H H H C H CH3 H C C H H CH3 H C C neopentyl H C H CH3 H CH3 H Naming of organic compound according to IUPAC system. Step 1) Find the longest continuous carbon chain and use the IUPAC name of the unbranched alkane as the basis. Add name of substituent as a prefix. Use base name with yl ending. Use replicating prefixes (di-, tri-, tetra-, etc.) according to the number of substituents attached to the main chain. Number the chain from the end nearest the substituent, and identify the carbon to which the substituent is attached by number. List substituents iin alphabetical order. List substituents n alphabetical Step 2) Step 3) Step 4) Carbon Chain Length and Prefixes Used in the I.U.P.A.C Nomenclature System Naming Alkanes C-C-C-C–C–C Six carbon atoms in longest chain used base name of hex All carbon and hydrogen with single bonds use ane ending Name of compound is hexane (CH3)2CHCH(CH3)2 (CH 2,3-Dimethylbutane (CH3)3CCH2CH3 2,2-Dimethylbutane Use replicating prefixes (di-, tri-, tetra-, etc.) according to the number of identical substituents attached to the main chain. 1 H3C H C 2 H C 3 4 CH3 CH3 CH3 Longest C chain has 4 carbon – use but All C and H with single bonds – use Parent name: ane CH3 - on 2nd and 3rd carbon - dimethyl IUPAC name: 2,3-dimethylbutane Practice Exercise Give IUPAC name for the following compound CH3 H 3C 1 2 6 7 CH 2 CH 3 CH CH 3 C 3 CH 2 4 CH 2 5 CH3 Continuous Continuous C chain : Prefix : Suffix : Substituent : Locant : 7C hept - ane trimethyl 2, 2, 5 2,2,52,2,5-trimethylheptane Draw the structure of 3,5,5 - trimethyl heptane Start by drawing the longest carbon chain: C–C–C–C–C–C–C Answer: C 1 2 3 4 C 5 6 7 C–C–C–C–C–C–C C When different When 2 or more of different kind of substituents substituents present : the substituents are listed alphabetically the listed prefixes di, prefixes di, tri, tert … are ignored in except alphabetising except iso and neo CH3 1 2 CH CH3 3 CH2 4 CH CH2 CH3 5 CH2 6 CH3 methyl ethyl 4-ethyl-2-methyl…. ethyl- methyl… Practice Practice Exercise CH3 H3C 1 2 3 4 5 6 5 C CH3 CH2 CH CH2 CH3 CH2 6 CH3 Continuous Continuous C chain : Prefix : Suffix : Substituent : 6C hex - ane 4-ethyl-2,2-dimethylhexane ethyl-2,2- dimethyl& ethyl When When 2 chains of equal length compete for chain selection as parent chain, choose the chain with the the greater number of substituents CH3 H3C CH2 CH CH CH2 CH2 CH3 CH3 CH CH3 CH CH3 2,3,5-trimethyl-4-propylheptane (4 substituents) CH3 H3C CH2 CH CH CH2 CH3 CH CH3 CH CH3 4-sec-butyl-2,3-dimethylheptane (3 substituents) CH2 CH3 When When first branching occurs at an equal distance from either end of the longest chain, choose the lower name that gives the lower number at the first point of different CH3 H3C 6 5 CH 4 CH2 3 CH CH3 2 CH 1 CH3 CH3 2,3,52,3,5-trimethylhexane CH3 H3C 1 2 CH 3 CH2 4 CH CH3 5 CH 6 CH3 CH3 2,4,52,4,5-trimethylhexane Polyfunctional Polyfunctional organic compounds contain different many different kinds of functional groups The proper suffix is determined by : i. ii. ii. identifying all the functional groups present principal highest then choose the principal group of highest priority priority Name parts: Name for polyfunctional groups consist of 4 parts: i. Suffix : identifies the principal functional group identifies principal class class to which the molecule belongs ii. iii. Parent : identifies the size of the main chain/ring size of Prefix : identifies what substituents are located what on the main chain/ring iv. iv. Locants : tells where substituents are located on where the main chain/ring Example Example of Polyfunctional Groups parent H3C 1 CH 2 OH 3 CH2 CH2 4 CH2 5 NH2 prefix Higher priority ∴ suffix amino5- aminopentan-2-ol @ 5-amino-2-pentanol Practice Practice Exercise suffix H3C CH CH3 CH3 prefix CH2 CH3 Methylpropane suffix H3C CH CH2 CH3 prefix Ethyl cyclohexane Cyclopropyl butane Structural Isomer Structural Isomer All have same formula but different structures and properties C4H10 H3C CH3 H C CH3 H2 C C H2 CH3 butane CH3 2-methylpropane Structural Isomer C5H12 Number of Constitutionally Isomeric Alkanes Isomeric CH4 C 2H 6 C 3H 8 C4H10 C5H12 C6H14 C7H16 1 1 1 2 3 5 9 C8H18 C9H20 C10H22 C15H32 C20H42 C40H82 18 35 75 4,347 366,319 62,491,178,805,831 • Number of isomeric alkanes Number increases as the number of carbons increase. carbons • There is no simple way to predict There how many isomers there are for a how particular molecular formula. Cycloalkanes Naming of Cycloalkanes • Name any alkyl groups on the ring in the usual way. CH2CH3 Ethylcyclopentane Ethylcyclopentane • List substituents in alphabetical order and count in the direction that gives the lowest number. H3C CH3 3-Ethyl- 1,1-dimethylcyclohexane CH2CH3 IUPAC Nomenclature of Cycloalkanes Named cyclo Named by placing the prefix cyclo to the corresponding alkanes Examples CH 2 H 2C CH 2 H 2C CH 2 H 2C CH 2 Cyclopropane Cyclobutane If only not If only one substituent present : not necessary to designate its position Example suffix prefix 6C 1 CH3 hexane Methyl cyclo hexane When substituents When 2 substituents present : i. beginning Numbered the C beginning with substituent substituent according to the alphabetical order Numbered in the way that gives the next next substituent the lowest number possible ii. Example 1 3 2 Methyl CH 3 1 cyclohexane 1-ethyl-2-methyl cyclohexane ethyl- 4 5 6 CH 2 CH 3 Ethyl 5 4 3 6 CH 3 1 CH 2 CH 3 2 1-ethyl-6-methylcyclohexane ethyl- Practice Exercise Give Give IUPAC names for the following cycloalkanes : CH3 H3 C H3C CH3 1,4-dimethylcyclohexane 1,4CH2 CH3 Isopropylcyclobutane 1-ethyl-3-methylcyclopentane ethyl- CH3 single When single ring is attached to a chain with greater greater no. of C atoms : cycloalkyl named as cycloalkylalkane 5 C chain CH2 CH2 CH2 CH2 CH3 1 2 3 4 5 parent 4C 4C chain substituent 1- cyclo butyl pentane butyl When more When more than 1 ring is attached to a single chain chain : cycloalkyl also named as cycloalkylalkane straight chain parent CH2CH2CH2 3 1 2 substituent groups 1,31,3- di cyclo hexyl propane Alkane Physical Properties Non – polar molecules Not – soluble in water Low density Low melting point Low boiling point These goes up as the number of carbons increase Practice Exercise Arrange Arrange the following compounds in order of increasing boiling point CH3CH2CH3 propane CH CH3CH2CH2CH2CH3 n-pentane Boiling point increases CH3( CH2)7 CH3 n-nonane and cycloalkane Naphtha (bp 95-150 ° C) C5-C12 5 12 Light gasoline (bp: 25-95 ° C) Kerosene (bp: 150-230 ° C) C12-C15 12 15 Crude oil C15-C25 15 25 Gas oil (bp: 230-340 ° C) Refinery gas C1-C4 1 4 Residue Industrial Fractioning Column Petroleum refining • Cracking – converts high molecular weight hydrocarbons to more useful, low molecular weight ones i) thermal cracking (by heat) ii) catalytic cracking (with the aid of catalyst) • – – Reforming increases branching of hydrocarbon chains branched hydrocarbons have better burning characteristics for automobile engines Catalytic cracking in laboratory scale Synthesis of alkanes Hydrogenation of alkenes An addition An example of addition reaction H C H alkene H C H + H H2 Pt / Pd / Ni H C H H H C H hydrogen alkane Example: C2H4 + H2 → C2H6 ethene ethane Ni Hydrolysis of Grignard reagent (alkylmagnesium halide) RMgX + H2O → RH + Mg(OH)X alkylmagnesium halide alkane H+ Example: CH3CH2CH2MgCl + H2O Propylmagnesium chloride H+ CH3CH2CH3 + Mg(OH)Cl Mg(OH)Cl Propane Wurtz reaction (Reduction of alkyl halide) 2RX + Na → R-R + 2NaX alkyl halide reducing agent alkane Example: 2CH3CH2CH2Br + 2Na → CH3CH2CH2CH2CH2CH3 + 2NaBr bromopropane hexane Reaction of Alkanes Light/heat ...
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