Chapter 8 Alkenes and alkynes I. Properties and synthesis 8.1 Introduction Alkenes are hydrocarbons whose molecules contain the carbon-carbon double bond. Hydrocarbons whose molecules contain the carbon-carbon triple bond are called alkynes.

8.2 Nomenclature of alkenes and cycloalkenes

The IUPAC rules for naming alkenes are similar in many respects to those for naming alkanes 1.Selecting the longest chain that contains the double bond 2.Number the chain

3. Indicate the locations of the substituent groups

4. Number substituted cycloalkenes in the way that gives the carbon atoms of the double bond the 1- and 2- positions and that also gives the substituent groups the lower numbers at the first point of difference

5. Two frequently encountered alkenyl groups are the vinyl group and the allyl group.

6. Designate the geometry of a double bond of a disubstituted alkene with the prefixes cis- and trans-

8.2A The ( E )-( Z ) System for designation alkene diastereomers

8.3 Nomenclature of alkynes 8.3A IUPAC Nomenclature Unbranched alkynes, for example, are named by replacing the –ane of the name of the corresponding alkane with the ending –yne. The chain is numbered in order to give the carbon atoms of the triple bond the lower possible numbers.

8.4 Physical properties of alkenes and alkynes 8.5 Hydrogenation of alkenes

8.6 Hydrogenation: The function of the catalyst

Catalytic hydrogen and Syn-- addition

8.6A Syn and anti additions

8.7A Syn addition of hydrogen: Synthesis of cis-alkenes

8.7B Anti addition of hydrogen: Synthesis of trans-alkenes

8.9 Relative stabilities of alkenes 8.9A Heats of hydrogenation

The order of stabilities;

8.9B Relative stabilities from heats of combustion

8.9C Overall relative stabilities of alkenes

8.10 Cycloalkenes The rings of cycloalkenes containing five carbon atoms or fewer exist only in the cis form. Therefore, fewer exist in the trans form because of the ring strain.

Cis- and trans-Cycloalkenes

8.11 Synthesis of alkenes via elimination reactions

8.12 Dehydrohalogenation of alkyl halides

8.12A E2 reactions: The orientation of the double bond in the product. Zaltsev’s Rule ( 查依采夫规则） 查依采夫规则 ---- 主要产物是双键连有烃基较多的。

8.12C The stereochemistry of E2 reactions:

8.13 Dehydration of alcohols 1.The experimental conditions----temperature and acid concentration

Ease of Dehydration

8.13A Mechanism of alcohol dehydration: An E1 reaction

Ease of dehydration for E1 reaction

8.15 Carbocation stability and the occurrence of molecular rearrangements ( 正碳离子的稳 定性和分子的重排的发生）

The type of rearrengement

Rearrengement mechanism (E1 reaction)

8.16 Alkenes by debromination of vicinal dibromides

8.17 Summary of methods for the preparation of alkenes

2. Dehydration of alcohols

3. Dehalogenation of vic- dibromides

4. Hydrogenlation of alkynes

8.18 Synthesis of alkynes by elimination reaction

8.19 The Acidity of terminal alkynes The hydrogen atoms of ethyne are considerably more acidic than those of ethene or ethane

Relative acidity;

Relative Acidity 共轭酸（ Conjugate acid) 越强，其共轭碱 (Conjugate base) 越弱。

8.20 Replacement of the acetylenic hydrogen atom of terminal alkynes （末端炔烃的氢原子被取代） Sodium ethynide and other sodium alkynides can be prepared by treating terminal alkynes with sodium amide (NaNH 2 ) in liquid ammonia

It applied synthesis (S N 2)

8.21 Other metal acetylides Ethyne and terminal alkynes also form metal derivatives with silver and copper (I) ions

As a method for separating terminal alkynes from alkynes that have an internal triple bond 区别末端的炔烃和叁键在中间的炔烃

Homework; 8.22, 8.24, 8.25, 8.29, 8.30 Happy New Year! Good luck for you final organic chemistry test!