有机化学OrganicChemistry李Chapter7_LIJI_简版.ppt

Chapter 7,1,Organic Chemistry,Shenzhen Graduate School of Harbin Institute of Technology,Chapter 7,2,A1. General features:,s C-C bond = 83 kcal/mol p C-C bond = 66 kcal/mol 149 kcal/mol,A weak p bond gives alkenes their reactivity,A. Structure and Bonding,Chapter 7,3,A3. Relative stabilities of alkenes Substitution effects General rule: the more alkyl groups there are around the C=C, the more stable the alkene is.,The most stable hexene is the most substituted one,Chapter 7,4,b. Conjugation effects adjacent C=C bonds are stabilized,,,More stable,More stable,Chapter 7,5,B1. Common names:,B2. Group names,B. Nomenclature:,,,Chapter 7,6,a. Take the alkane name and drop the second “a” and “e” to form alkene name. b. Number the chain to give the lowest number for the start of the C=C. c. For two C=C bonds - drop “ne” of alkene name and add “diene”. For three C=C bonds - drop “ne” of alkene name and add “triene”… d. The double bond is always given preference in numbering. e. For cycloalkenes it is always assumed that the C=C bond starts in the “1” position.,B3. IUPAC names,Chapter 7,7,B3. cis and trans nomenclature: A comparison of the same two groups on either side of the C=C bond,,• Remember that cis cannot go to trans without a gigantic cost of energy - break the p bond.,Chapter 7,8,B4. E-Z nomenclature:,E,E,E,Z,Z,Z,Uses the Cahn-Ingold-Prelog priority scheme (1) Assign priorities to the sustituents around the C=C bond (2) Determine the relative positions for the two top groups in terms of priority for each side of the C=C bond,Chapter 7,9,C. Uses of alkenes,Chapter 7,10,D1. Dehydrohalogenation - via E2 mechanism,b. synthetic considerations (1) 3o alkyl halides are best (can’t undergo SN2) (2) use a bulky base,t-butoxide,triethylamine,proton sponge,2, 6-dimethylpyridene,D. Preparation of alkenes,a. general reaction,Chapter 7,11,D3. Dehydration of alcohols,,driven off by heat or absorbed by zeolites, etc.,a. general reaction:,Chapter 7,12,b. mechanism,• setup leaving group,• actually E1 or E2,Note: acid catalyzed rearrangements with E1 possible,Chapter 7,13,1. Know how to calculate elements of unsaturation. 2. What the p bond in olefins is and does - relative stability. 3. Nomenclature: a. general rules b. cis/trans and E/Z names 4. Preparation of alkenes: a. dehydrohalogenation - mechanism c. dehydration of alcohols - mechanism (adjust to E1 or E2).,E. Summary,。