Chapter 3 AN INTRODUCTION TO ORGANIC COMPOUNDS NOMENCLATURE, PHYSICAL PROPERTIES, REPRESENTATION OF STRUCTURE AND

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1 ORGANIC CHEMISTRY, 2 ND EDITION PAULA YURKANIS BRUICE Chapter 3 AN INTRODUCTION TO ORGANIC COMPOUNDS NOMENCLATURE, PHYSICAL PROPERTIES, AND REPRESENTATION OF STRUCTURE RAED M. AL-ZOUBI, ASSISTANT PROFESSOR OF CHEMISTRY DEPARTMENT OF CHEMISTRY - N 4 L 0 JORDAN UNIVERSITY OF SCIENCE AND TECHNOLOGY

2 Alkanes are hydrocarbons containing only single bonds General formula: C n H 2n+2 2

3 3

4 Isomers: 1. Constitutional (Structural) isomers have the same molecular formula, but their atoms are linked differently 4

5 Nomenclature of Alkyl Substituents Removing a hydrogen from an alkane results in an alkyl substituent 5

6 If a hydrogen is replaced by an OH, the compound becomes an alcohol; if it is replaced by an NH 2, the compound becomes an amine; 6

7 If it is replaced by a halogen, the compound becomes an alkyl halide; and if it is replaced by an OR, the compound becomes an ether Some common names are derived from the alkyl groups 7

8 Different Kinds of Carbons and Hydrogens 8

9 A compound can have more than one name, but a name must specify only one compound The prefix tert is used for tert-butyl and tert-pentyl compounds 9

10 The use of an iso prefix: 10

11 Nomenclature of Alkanes 1. Determine the number of carbons in the longest continuous chain 11

12 2. Number the chain so that the substituent gets the lowest number 3. Number the substituents to yield the lowest possible number in the number of the compound substituents are listed in alphabetical order 12

13 4. Assign the lowest possible numbers to all of the substituents 5. If the same substituent numbers are obtained in both directions, the first group cited receives the lower number 13

14 6. If a compound has two or more chains of the same length, the parent hydrocarbon is the chain with the greatest number of substituents 7. Certain common nomenclatures are used in the IUPAC system 14

15 Some substituents have only a systematic name 15

16 Systematic Naming of Substituents Systematic Method 1. Determine longest chain starting with the point of attachment. 2. Name longest chain as alkyl. 3. Number and name substituents and add to alkyl as prefix. 4. Name the substituent as (#-alkylalkyl). The parentheses distinguish substituent numbering from the numbering of the longest chain. 16

17 Nomenclature of Cycloalkanes 1. No number is needed for a single substituent on a ring 2. Name the two substituents in alphabetical order 17

18 3. If there are more than two substituents, they are cited in alphabetical order 18

19 Nomenclature of Alkyl Halides In the IUPAC system, alkyl halides are named as substituted alkanes 19

20 Structures of Alkyl Halides 20

21 Conformations of Alkanes: Rotation about Carbon Carbon Bonds 21

22 Different Conformations of Ethane 22

23 A staggered conformer is more stable than an eclipsed conformer 23

24 Conformations of n-butane 24

25 Steric strain: repulsion between the electron clouds of atoms or groups The gauche interaction destabilizes the gauche conformation 25

26 Q: What is the relationship between the Newman representations shown? A) identical B) constitutional isomers C) Conformational isomer D) stereoisomers

27 Q: What is the relationship between the Newman representations shown? A) identical B) constitutional isomers C) Conformational isomer D) stereoisomers

28 Q: What is the relationship between the Newman representations shown? A) Identical B) constitutional isomers C) Conformational isomer D) stereoisomers

29 Q: What is the relationship between the Newman representations shown? A) Identical B) constitutional isomers C) Conformational isomer D) stereoisomers

30 Q: Select the least stable conformation of ethylene glycol. A) B) C) D)

31 Q: Select the least stable conformation of ethylene glycol. A) B) C) D)

32 Q: Select the most stable conformation of butanoic acid. A) B) C) D)

33 Q: Select the most stable conformation of butanoic acid. A) B) C) D)

34 Q: What is the relationship between the Newman representations shown? A) identical B) constitutional isomers C) Conformational isomer D) stereoisomers

35 Q: What is the relationship between the Newman representations shown? A) identical B) constitutional isomers C) Conformational isomer D) stereoisomers

36 Q: What is the IUPAC name for the compound represented by the Newman projection? A) 1-tert-Butyl-1-isopropylethane B) 1-tert-Butyl-3-methylbutane C) 2-isopropyl-3,3-dimethylbutane D) 2,2,3,4-tetramethylpentane

37 Q: What is the IUPAC name for the compound represented by the Newman projection? A) 1-tert-Butyl-1-isopropylethane B) 1-tert-Butyl-3-methylbutane C) 2-isopropyl-3,3-dimethylbutane D) 2,2,3,4-tetramethylpentane

38 Cycloalkanes: Ring Strain Angle strain results when bond angles deviate from the ideal bond angle 38

39 The chair conformation of cyclohexane is free of strain 39

40 Ring Flipping in Cyclohexane 40

41 Drawing Cyclohexane 41

42 The Conformations of Cyclohexane and Their Energies 42

43 Conformations of Monosubstituted Cyclohexanes 43

44 44

45 Steric Strain of 1,3-Diaxial Interaction in Methylcyclohexane 45

46 The larger the substituent on a cyclohexane ring, the more the equatorial substituted conformer will be favored K eq = [equatorial conformer]/[axial conformer] 46

47 The Chair Conformers of cis- or trans- 1,4-Dimethylcyclohexane 47

48 48

49 49

50 1-tert-Butyl-3-Methylcyclohexane 50

51 Q: Which compound has the greatest torsional strain in the planar conformation? A) Cyclopropane B) Cyclobutane C) Cyclopentane D) cyclohexane

52 Q: The most stable conformation of cis-1- tert-butyl-4-methylcyclohexane has A) both groups equatorial B) both groups axial C) the tert-butyl group axial and the methyl equatorial D) the tert-butyl group equatorial and the methyl axial

53 Q: The most stable conformation of trans- 1-isopropyl-3-methylcyclohexane is: A) B) C) D)

54 Q: What is the relationship between the two chair conformations below? A) conformational isomers B) constitutional isomers C) different compounds D) stereoisomers

55 Q: What is the relationship between the two cyclohexane chairs below? A) conformational isomers B) constitutional isomers C) Stereoisomers D) different compounds

56 Q: Which of the following statements is not true concerning the chair-chair interconversion of trans-1,2- diethylcyclohexane? A) An axial group will be changed into the equatorial position. B) The energy of repulsions present in the molecule will be changed. C) Formation of the cis substance will result. D) One chair conformation is more stable than the other

57 Q: Which of the listed terms best describes the relationship between the methyl groups in the chair conformation of the substance shown? A) Eclipsed B) Trans C) Anti D) Gauche

58 Q: Which of the following has an equatorial methyl group in its most stable conformation? A) B) C) D)

59 Q: Which of the following statements best describes the most stable conformation of trans-1,3-dimethylcyclohexane? A) Both methyl groups are axial. B) Both methyl groups are equatorial. C) One methyl groups is axial, the other equatorial. D) The molecule is severely strained and cannot exist.

60 Q: What is the relationship between the two structures shown? A) Constitutional isomers B) Stereoisomers C) Different drawings of the same conformation of the same compound. D) Different conformations of the same compound.

61 Q: The most stable conformation of the compound to the right has A) an axial methyl group and an axial ethyl group. B) an axial methyl group and an equatorial ethyl group. C) an equatorial methyl group and an equatorial ethyl group. D) an equatorial methyl group and an axial ethyl group.