Chapter 4 Alkanes and Cycloalkanes. Structure, Nomenclature and Conformations

Transcription

1 hapter 4 Alkanes and ycloalkanes Structure, Nomenclature and onformations

2 hapter 4 arbon Bonding

3 ydrocarbons The Simplest lass of Organic ompounds A. ontain only arbon and ydrogen B. arbon can bond in different ways 4

4 ydrocarbons The Simplest lass of Organic ompounds B. arbon can bond in different ways (multiple bonds) 24 22

5 Structural Representation of Simple Alkanes Name Kekule structure ondensed structure Model methane 4 ethane 33 propane 323 butane 3223 Simple alkanes have the general formula n2n+2.

6 ydrocarbons The Simplest lass of Organic ompounds. ydrocarbons are further subclassified SATURATED UNSATURATED ALIPATI AROMATI

7 Nomenclature of Alkanes

8 Formulas and Properties of Normal Alkanes n Molecular ondensed Name Melting Boiling Formula Structural Formula point ( o ) point ( o ) methane ethane propane butane pentane hexane heptane octane nonane decane

9 1º, 2º, 3º, and 4º arbons A carbon atom is classified as primary (1º), secondary (2º), tertiary (3º), or quaternary (4º) depending upon whether or not it is directly bonded to a total of one, two, three, or four other carbon atoms, respectively. 1 º 2 º 3 º 4 º

10 1º, 2º, 3º, and 4º arbons - Examples Indicate the number of primary, secondary, tertiary, and quaternary carbons in the following molecules: 1º: 5 2º: 2 3º: 1 4º: 1 1º: 2 2º: 2 3º: 2 4º: 0

11 ydrocarbon Nomenclature Why is the IUPA system Necessary? onsider the following carbon hydrides Each formula represents a unique compound. When structural formulas are considered, however, 37 has only 1 isomer. 410 has 2 isomers. 512 has 3 isomers. 614 has 5 isomers has 75 isomers has 4 x 10 9 isomers.

12 ydrocarbon Nomenclature Basis of the IUPA System of naming-the Root Name 1. The root name of a compound is derived from the longest continuous chain of carbon atoms or the longest continuous chain of carbon atoms containing a given special structural feature. a. ommon stems are used to indicate the length of carbon chains. meth-, eth-, pro-, but-, pent-, hex-, hept-, oct-, non-, dec- b. ommon suffixes indicate the class of compounds. Alkane Alkene Alkyne

13 ydrocarbon Nomenclature 2. If the carbon chain contains unsaturation (double or triple bonds), the carbon chain is numbered so as to give double or triple bond(s) the lowest number(s) Butene 2-Butene Butene 1-Butene

14 ydrocarbon Nomenclature Substituents may be attached to a carbon chain 1. Substituents which are not pieces of alkanes: F- Fluoro- -NO2 Nitro l- hloro- -N2 Amino Br- Bromo- -O ydroxy I- Iodo-

15 ydrocarbon Nomenclature 2. Substituents which are pieces of alkanes - Alkyl groups Names are derived from the parent alkanes. Parent alkane When attached to another chain Parent hain Methane Methyl- BASE NAME Parent hain Ethane Ethyl- BASE NAME

16 ydrocarbon Nomenclature 2. Substituents which are pieces of alkanes - Alkyl groups Parent alkane When attached to another chain Parent hain Propane Propyl- BASE NAME Also called a methyl ethyl group Parent hain Isopropyl- BASE NAME

17 ydrocarbon Nomenclature -Alkyl Groups Parent hain butyl- BASE NAME Parent hain s-butyl- BASE NAME butane Also called a 1-methyl propyl group

18 ydrocarbon Nomenclature -Alkyl Groups 2-methylpropane ( isobutane ) Parent hain Parent hain isobutyl- BASE NAME Also called a 2-methyl propyl group t-butyl- BASE NAME Also called a dimethyl ethyl group

19 ydrocarbon Nomenclature -Alkyl Groups Name Formula Line structure (3) (3)22- (3)3- methylethylpropylisopropyln-butyls-butylisobutylt-butyl-

20 hapter 4 Alkanes and ycloalkanes Nomenclature-Putting the Pieces Together

21 ydrocarbon Nomenclature -Final Step Position of Attachment ( Locant ) of Substituents is Indicated 1. For carbon chains with double or triple bonds (alkenes and alkynes), the numbering system for the base carbon chain has already been established and does not change. 2. For saturated carbon chains (alkanes) the numbering system for the base carbon chain is determined by the positions of the substituents. Substituent names (in alphabetical order) and numbers are added (prefixed) to the base name of the compound.

22 ydrocarbon Nomenclature Putting it Together for a Simple Alkane Position of alkyl groups Family 4-isopropyl-3-methyl heptane Base name Alkyl groups Longest chain

23 ydrocarbon Nomenclature A more complicated example l l 2 l l l 2 l l 3 l l 1,3,5-trichloro-5-isobutyl-3,9-dimethyl decane 1,3,5-trichloro-3,9-dimethyl-5-(2-methylpropyl) decane

24 Name the following compound isopropylpentane 3-ethyl-2-methylpentane

25 Draw the structure of 3-ethyl-6-isopropyl-3,7-dimethyldecane.

26 Name the following compound: 1 7 * 3-isopropyl-2,2,6-trimethyl-heptane

27 ydrocarbon Nomenclature -Other arbon Groups Main chain Main chain Main chain Main chain Main chain cyclopropyl - cyclobutyl - cyclopentyl - cyclohexyl - phenyl -

28 ydrocarbon Nomenclature -yclic Alkanes 1. Structures are usually abbreviated 2. Planar representations do not represent 3-D shape.

29 ydrocarbon Nomenclature -yclic Alkanes 3. yclic structures are numbered and named to give the lowest numbers to substituents ,2-dimethylcyclopentane 3 1,2,4-trimethylcyclohexane

30 Draw the structure of 1-sec-butyl-3-isopropylcyclopentane (1-methylethyl)-3-(1-methylpropyl)cyclopentane

31 Nomenclature of Bicyclic ompounds bicyclo [4.4.0] decane bicyclo [3.3.2] decane bicyclo [6.2.0] decane spiro [4,5] decane

32 I 1-cyclobutyl-2-iodo-4-isobutyl cyclohexane I 5-iodo-7-isobutyl spiro[3,5]nonane I 2-iodo-4-isobutyl bicyclo[4.2.0]octane

33 cubane basketane housane churchane

34 hapter 4 Isomerism Revisited

35 Isomerism n-butane butane iso-butane 2-methylpropane

36 Isomerism Two ompounds Are the connectivities of the atoms the same? Are the chemical formulas the same? Yes No The compounds are not isomers. Yes No The compounds are constitutional isomers. Are the compounds superimposable? No Yes The compounds are stereoisomers. The compounds are identical. Are the compounds mirror images? Yes No The compounds are enantiomers. The compounds are diastereomers.

37 Isomerism What is the relationship between these two molecules? 2,3-dimethylpentane 2,3-dimethylhexane

38 Isomerism What is the relationship between these two molecules? and 2,4-dimethylpentane 2,2-dimethylpentane

39 Isomerism What is the relationship between these two molecules? 2,3-dimethylpentane 2,3-dimethylpentane

40 Question: Are pentane and cyclopentane isomers???

41 yclic Alkanes - cis/trans Isomerism onsider the formula 510 There appear to be five constitutional isomers which do not contain a double bond:

42 yclic Alkanes - cis/trans Isomerism 1,2-Dimethylcyclopropane can actually exist as two geometric isomers: cis-1,2-dimethylcyclopropane trans-1,2-dimethylcyclopropane stereoisomers

43 ombustion of ydrocarbons

44 ombustion of ydrocarbons + O2 O O2 O2 + 2 O O2 O2 + 2 O O2 O2 + 2 O O2 O2 + 2 O O2 O2 + 2 O

45 ombustion of ydrocarbons n2n+2 + (n-alkane) (3n+1) 2 O2 no2 + (n+1) 2O + Δcomb (kj/mol) n Δcomb (kj/mol) Δcomb/ (kj/mol)

46 ombustion of ydrocarbons least stable O 2 8 O O º = kj/mol O 2 8 O O º = kj/mol most stable O 2 8 O O º = kj/mol 818

47 Sources of ydrocarbons

48 Boiling Points for Straight-hain Alkanes

49 Physical Properties of Alkanes The Basis for Fractional Distillation ot crude oil is fed in at the foot of the fractionating column and mixed with steam. Various constituents, or fractions, of the crude oil separate at various points of the column.

50 Physical Properties of Alkanes The Basis for Fractional Distillation # s

51 In general, the larger an alkane molecule, the more strongly it is attracted to other molecules through London dispersion forces. Alkanes composed of larger molecules are harder to melt than alkanes composed of smaller molecules. Alkanes with even numbers of carbon atoms fall on a melting point curve that is slightly higher than the melting point curve for alkanes with odd numbers of carbon atoms.

52 Uses of ydrocarbons