1. Bioorganic chemistry for General Medicine students Peoples’ Friendship University of Russia Faculty of Science L 2. Alkenes. Alkynes Groups ML-127/128 Moscow, 2016 Lecturer: Natalia

2. The nomenclature of alkenes and alkynes

3. The nomenclature of alkenes In naming alkenes: · 1. Name the parent hydrocarbon by locating the longest carbon chain that contains the double bond and name it according to the number of carbons with the suffix -ene. · 2. Number the carbons of the parent chain so the double bond carbons have the lowest possible numbers. · 3. If the double bond is equidistant from each end, number so the first substituent has the lowest number. · 4. Write out the full name, numbering the substituents according to their position in the chain and list them in alphabetical order. · 5. Indicate the double bond by the number of the first alkene carbon.

4. The nomenclature of alkenes and alkynes The names of univalent radicals derived from unsaturated acyclic hydrocarbons have the endings "-enyl", "-ynyl", "-dienyl", etc., the positions of the double and triple bonds being indicated where necessary. The carbon atom with the free valence is numbered as 1.

5. The nomenclature of alkynes The IUPAC names are obtained by dropping the ending –ane of the parent alkane and adding the suffix –yne. If necessary the carbon chain including the triple bond is numbered from the end nearest this bond. The position of the triple bond is indicated by prefixing the number of the carbon preceding it to the name of the alkyne Alkynes are sometimes named as derivatives of acetylene, the simplest alkyne. This form of naming is useful when referring to the conjugate bases of alkynes, such as acetylide ion

6. Alkene. Methods of preparation Dehydration of alcohols. When alcohol is heated in the presence of sulphuric acid at 140-180ºC, a molecule of water is eliminated Zaitsev rule: when alternative exist, hydrogen is preferentially eliminated from the carbon atom with fewer number of hydrogen atoms

7. Alkene. Methods of preparation Dehydrohalogenation of alkyl halides. When an alkyl halide is heated with an alcoholic solution of sodium or potassium hydroxide, a molecule of hydrogen halide is eliminated and an alkene is formed Controlled hydrogenation of alkynes

8. Alkynes. Methods of preparation

9. Chemical properties of alkenes Addition of hydrogen Alkenes add hydrogen under pressure and in the presence of Ni, Pt or Pd catalyst to produce saturated hydrocarbons. Addition of halogen Halogens (Cl 2 or Br 2 ) react with alkenes readily to give dihalogen derivatives

10. Chemical properties Addition of H-X (hydrogen halides) Relative rate of reactivity of HX: HI > HBr > HCl > HF The strongest acid, HI, is the most reactive because it can most readily lose H + to the π bond of the alkene. The acid therefore acts as an electrophile and attacks the electrons of the bond. Markovnikov's Rule: When an unsymmetrical alkene reacts with a hydrogen halide, the hydrogen adds to the carbon that has the greater number of hydrogens attached to it, and the halogen adds to the carbon having fewer hydrogens.

11. Chemical properties. Alkenes. Addition of the electrophile to an unsymmetrical alkene proceeds by way of the more stable carbocation.

12. Chemical properties. Alkenes. Anti-Markovnikov Addition of HBr Sometimes HBr adds to an alkene in such a way that the bromide becomes attached to the least substituted carbon. The formation of the anti-Markovnikov product has been observed when O 2 or peroxides (ROOR) are present in the reaction. These compounds readily form free radicals. These radicals can react with HBr to then generate bromine radicals by abstracting a hydrogen atom. Addition of HHal to alkene derivatives with electron-withdrawing groups (CF 3, COOH, NO 2 and etc.) attached to the double bond proceeds as anti Markovnikov’s addition.

13. Alkynes. Chemical Properties enol flame

14. Alkynes. Chemical Properties

15. Oxidation of Alkynes and Alkenes