Organic Chemistry for Students of Medicine and Biology 大学化学 III 和大学化学 III(2) March 4, 2015
Refining of petroleum, a major natural source of alkanes Chapter 4 Alkanes and Cycloalkanes ( 烷烃和环烷烃 ) March 3, 2015
C n H 2n+2 Homologous series and isomerism of alkanes Homologous series is a family of compounds in which each member differs from the next by one methylene (CH 2 ) group.
Isomerism Isomers : compds that have the same molecular formula but different structural formula, therefore they have the different chemical and physical properties. ( different compds with identical molecular formula are isomers.)
4.1.1 Nomenclature of Alkanes 1. Common names ( 普通命名法 ) 甲乙丙丁戊己庚辛壬癸 n-( 正 ); Iso-( 异 ); Neo-( 新 ) 2. Systematic Nomenclature (IUPAC names) International Union of Pure and Applied Chemistry
Alkane Nomenclature # Carbons Name 1 2 3 4 5 methane ethane propane butane pentane
Alkane Nomenclature # Carbons Name 6 7 8 9 10 hexane heptane octane nonane decane
C n H 2n+2 Methane CH 4 Ethane CH 3 CH 3 Propane CH 3 CH 2 CH 3 How many butanes are there?
Butanes n-butane CH 3 CH 2 CH 2 CH 3 b.p -0.4 o isobutane CH 3 CH 3 CH CH 3 b.p -10.2 o
How many pentanes are there?
Pentanes n-pentane CH 3 CH 2 CH 2 CH 2 CH 3 isopentane CH 3 CH 3 CH CH 2 CH 3 neopentane CH 3 CH 3 C CH 3 CH 3
Molecular Formula CH 4 C 2 H 6 C 3 H 8 Isomers 1 1 1 C 4 H 10 2 C 6 H 14 C 10 H 22 C 20 H 42 C 40 H 82 5 75 366,319 62,491,178,805.831
Alkyl Groups Alkane Alkyl CH 4 CH 3 - methane methyl
propyl CH 3 CH 2 CH 2 isopropyl CH 3 CH CH 3 isopropyl chloride CH 3 CHCl CH 3
n-butyl CH 3 CH 2 CH 2 CH 2 CH 3 isobutyl CH 3 CHCH 2 s-butyl CH 3 CHCH 2 CH 3 CH 3 t-butyl CH 3 C CH 3
CH 3 CH 3 C OH CH 3 t-butyl alcohol
What is the common name of this compound? CH 3 CH 3 CHCH 2 Cl isobutyl chloride
What is the common name of this compound? Isopropyl alcohol
What is the common name of this compound? OH CH 3 CH 2 CHCH 3 s-butyl alcohol
neopentyl CH 3 CH 3 CCH 2 CH 3 (CH 3 ) 3 CCH 2 OH neopentyl alcohol
IUPAC Names 1. Longest continuous chain as the parent chain. 2. Position by number 3. Number from end which gives the smallest numbers 4. Use di-, tri-, tetra- 5. Arrange in alphabetical order (except di-, tri-, tetra-, sec-, tert)
CH 3 CHCH 2 CH 3 CH 3 Common Name: isopentane IUPAC Name: 2-methylbutane
2-methylpentane CH 3 CHCH 2 CH 2 CH 3 CH 3 (Bond line formula)
IUPAC Name? 2,3-dimethylpentane
IUPAC Name? 2,3-dimethylpentane
IUPAC Name? 3-methylpentane
IUPAC Name? 3-methylpentane
CH 3 1 2 3 4 5 6 7 8 CH 3 CH 2 CH CH CH 2 CH CH 2 CH 3 CH 3 CH 2 CH 3 6-Ethyl-3,4-dimethyloctane
4-ethyl-3,5-dimethyloctane
CH 3 CH 3 CH 3 CH CH 2 CH CH 2 C CH 3 CH 3 CH CH 2 CH 3 CH 2 CH 3 4-Isopropyl-2,6,6-trimethylnonane
Cycloalkanes CH 3 H methylcyclopropane CH 2 CH 3 ethylcyclopentane cyclohexane
IUPAC Name? Methylcyclobutane
3-cyclopropylpentane
The types of carbon atom Primary carbon ; Secondary carbon ; Tertiary carbon; Quaternary carbon CH 3 C CH 2 C C C CH C C C C C C C 1 O 2 O 3 O 4 O
2.1.2 Conformation of alkane Different arrangements of atoms that result from rotation around a single bond are called conformations, and a specific conformation is called a conformatonal isomer (Conformer).
Conformations
CH 3 CH 3 Ethane
H Back H H H C C H H In the Out plane
H H H C - C H H H Wedge H H H H H Sawhorse H H H H H H H Newman
Newman Projection Formula Front carbon Back carbon 120 o
Rotate about C-C Bond
Staggered Conformation
Eclipsed Conformation
Conformations of n-butane CH 3 CH 2 -CH 2 CH 3 Rotate about this bond
Anti Gauche (Most stable) (In between)
H CH 3 CH3 H CH 3 H H H H H H CH 3 Gauche Anti
Nomenclature Alkanes Review Alkyl Groups Common Names IUPAC Names Conformation Conformational isomer
2.1.3 Chemical properties of alkanes C--C, C H bond energy; Bond polarity C n H 2n+2 + 3n+1 2 O 2 nco 2 + (n+1)h 2 O + 热能
Halogenations of alkanes are substitution reactions in which a halogen replaces one (or more) of the alkane s hydrogen atoms to give alkyl halides. C H + X 2 C X + HX
How does this reaction take place? CH 3 -H + Cl-Cl CH 3 -Cl + H-Cl 1. Stepwise? 2. Concerted?
How Break Bonds? X : Y 1. Ionic: X + :Y - heterolytic 2. Radical: X.. Y homolytic
No reaction when methane and chlorine are mixed Energy CH 4 + Cl 2 CH 3 Cl + HCl
Transition State + E N E Activation Energy R G Reactants Y Products Reaction Coordinate
Light makes reaction start CH Cl 2 Cl 4 2 CH 4 CH CH 4 4 Cl 2 Cl CH Cl 2 4 2 CH 4 Cl 2 CH 4 Cl Cl 2 2 Cl Cl 2 2 CH 4
Chlorine Cl 2
Cl light 2 2 Cl. CH 4 Cl 2 Cl 2 CH 4 CH CH 4 4 Cl 2 Cl.. Cl CH Cl 2 4 CH 4 Cl 2 CH 4 Cl Cl 2 2 Cl Cl 2 2 CH 4
Cl. + CH 4 HCl + CH 3. CH 4 Cl 2 Cl 2 CH 4 CH CH 4 4 Cl 2. Cl Cl CH. 2 3 HCl CH 4 Cl 2 CH 4 Cl Cl 2 2 Cl Cl 2 2 CH 4
Transition State δ δ.. Cl... H... CH 3
CH 3. + Cl 2 CH 3 Cl + Cl. CH 4 Cl 2 Cl 2 CH 4 CH CH 4 4 Cl 2. Cl Cl CH 2 3 HCl CH Cl 4 Cl. CH 4 Cl Cl 2 2 Cl Cl 2 2 CH 4
Initiation Step: Determining-rate step Propagation Steps:
Chain-Terminating Steps
Regioselectivity Cl 2 CH 3 CH 2 CH 2 CH 3 light 28% 72%
Cl 2 CH 3 CH 2 CH 2 CH 3 light CH 3 CH 2 CH 2 CH 3 CH 3 CH 2 CHCH 3 primary radical secondary radical
CH 3 CH 2 CH 2. + H.. CH 3 CHCH 3 + H. 410 KJ/mol 98 kcal/mol 397 KJ/mol 95 kcal/mol Bond dissociation energy CH 3 CH 2 CH 3
H CH 3 -C-CH 2 -H CH 3 H CH 3 -C-CH 2. CH 3 H.. CH 3 -C-CH 2 -H CH 3 410 KJ/Mole 380 KJ/Mole
Relative Stability R 3 C. > R 2 CH. > RCH. 2 Relative Rate of Chlorination R 3 CH 5.2 R 2 CH 2 3.9 RCH 3 1.0
What is the major product? CH 3 CH 3 CHCH 3 Cl 2 light
CH 3 CH 3 CHCH 3 Cl 2 light CH 3 CH 3 CCH 3 CH 3 CH 3 CHCH 2 Cl Cl 36% 64%
Br 2 CH 3 CH 2 CH 3 light Br CH 3 CH 2 CH 2 Br CH 3 CHCH 3 3% 97%
CH 3 CH 2 CH 2 CH 3 Br 2 light 2% 98%
Relative Rate Bromination R 3 CH > R 2 CH 2 > RCH 3 1640 82 1
More Reactive Less Selective
The order of halogen reactivity F 2 >Cl 2 >Br 2 >I 2
How do you make: CH 3 CH 3 CCH 3 Br t-butyl bromide
Br 2 CH 3 CH 3 CH 3 CCH 3 CH 3 CHCH 3 light Br
Cl 2 Light Cl H
The stability of radicals The alkyl radical is sp 2 hybridization. the stability sequence of them is 3 o >2 o >1 o > CH 3 Trigonal planar The p orbital contains the unpaired electron Methyl radical
Chinese book: P65 Free radicals
Summary Free Radical reaction Initiation Propagation Termination Relative Radical Stability Tertiary>Secondary>Primary GJX-2015