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
Alkanes are hydrocarbons containing only single bonds General formula: C n H 2n+2 2
3
Isomers: 1. Constitutional (Structural) isomers have the same molecular formula, but their atoms are linked differently 4
Nomenclature of Alkyl Substituents Removing a hydrogen from an alkane results in an alkyl substituent 5
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
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
Different Kinds of Carbons and Hydrogens 8
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
The use of an iso prefix: 10
Nomenclature of Alkanes 1. Determine the number of carbons in the longest continuous chain 11
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
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
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
Some substituents have only a systematic name 15
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
Nomenclature of Cycloalkanes 1. No number is needed for a single substituent on a ring 2. Name the two substituents in alphabetical order 17
3. If there are more than two substituents, they are cited in alphabetical order 18
Nomenclature of Alkyl Halides In the IUPAC system, alkyl halides are named as substituted alkanes 19
Structures of Alkyl Halides 20
Conformations of Alkanes: Rotation about Carbon Carbon Bonds 21
Different Conformations of Ethane 22
A staggered conformer is more stable than an eclipsed conformer 23
Conformations of n-butane 24
Steric strain: repulsion between the electron clouds of atoms or groups The gauche interaction destabilizes the gauche conformation 25
Q: What is the relationship between the Newman representations shown? A) identical B) constitutional isomers C) Conformational isomer D) stereoisomers
Q: What is the relationship between the Newman representations shown? A) identical B) constitutional isomers C) Conformational isomer D) stereoisomers
Q: What is the relationship between the Newman representations shown? A) Identical B) constitutional isomers C) Conformational isomer D) stereoisomers
Q: What is the relationship between the Newman representations shown? A) Identical B) constitutional isomers C) Conformational isomer D) stereoisomers
Q: Select the least stable conformation of ethylene glycol. A) B) C) D)
Q: Select the least stable conformation of ethylene glycol. A) B) C) D)
Q: Select the most stable conformation of butanoic acid. A) B) C) D)
Q: Select the most stable conformation of butanoic acid. A) B) C) D)
Q: What is the relationship between the Newman representations shown? A) identical B) constitutional isomers C) Conformational isomer D) stereoisomers
Q: What is the relationship between the Newman representations shown? A) identical B) constitutional isomers C) Conformational isomer D) stereoisomers
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
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
Cycloalkanes: Ring Strain Angle strain results when bond angles deviate from the ideal 109.5 bond angle 38
The chair conformation of cyclohexane is free of strain 39
Ring Flipping in Cyclohexane 40
Drawing Cyclohexane 41
The Conformations of Cyclohexane and Their Energies 42
Conformations of Monosubstituted Cyclohexanes 43
44
Steric Strain of 1,3-Diaxial Interaction in Methylcyclohexane 45
The larger the substituent on a cyclohexane ring, the more the equatorial substituted conformer will be favored K eq = [equatorial conformer]/[axial conformer] 46
The Chair Conformers of cis- or trans- 1,4-Dimethylcyclohexane 47
48
49
1-tert-Butyl-3-Methylcyclohexane 50
Q: Which compound has the greatest torsional strain in the planar conformation? A) Cyclopropane B) Cyclobutane C) Cyclopentane D) cyclohexane
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
Q: The most stable conformation of trans- 1-isopropyl-3-methylcyclohexane is: A) B) C) D)
Q: What is the relationship between the two chair conformations below? A) conformational isomers B) constitutional isomers C) different compounds D) stereoisomers
Q: What is the relationship between the two cyclohexane chairs below? A) conformational isomers B) constitutional isomers C) Stereoisomers D) different compounds
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
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
Q: Which of the following has an equatorial methyl group in its most stable conformation? A) B) C) D)
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.
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.
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.