Đang chuẩn bị liên kết để tải về tài liệu:
Lecture Organic chemistry: Chapter 7 - L. G. Wade, Jr.

Chapter 7 - Structure and synthesis of Alkenes. The goal in this chapter: Draw and name alkenes and cycloalkenes; given a molecular formula, calculate the number of double bonds and rings; explain how the stability of alkenes depends on their structures; show how alkenes can be synthesized by eliminations from alkyl halides and alcohols. | Chapter 7 ©2010, Prentice Hall Organic Chemistry, 7th Edition L. G. Wade, Jr. Structure and Synthesis of Alkenes Chapter 7 Introduction Alkenes are hydrocarbon with carbon-carbon double bonds. Alkenes are also called olefins, meaning “oil-forming gas”. The functional group of alkenes is the carbon-carbon double bond, which is reactive. Chapter 7 Sigma Bonds of Ethylene Chapter 7 Orbital Description Sigma bonds around the double-bonded carbon are sp2 hybridized. Angles are approximately 120º and the molecular geometry is trigonal planar. Unhybridized p orbitals with one electron will overlap forming the double bond (pi bond) . Chapter 7 Bond Lengths and Angles sp2 hybrid orbitals have more s character than the sp3 hybrid orbitals. Pi overlap brings carbon atoms closer shortening the C—C bond from 1.54 Å in alkanes down to 1.33 Å in alkenes. Chapter 7 Pi Bonding in Ethylene The pi bond in ethylene is formed by overlap of the unhybridized p . | Chapter 7 ©2010, Prentice Hall Organic Chemistry, 7th Edition L. G. Wade, Jr. Structure and Synthesis of Alkenes Chapter 7 Introduction Alkenes are hydrocarbon with carbon-carbon double bonds. Alkenes are also called olefins, meaning “oil-forming gas”. The functional group of alkenes is the carbon-carbon double bond, which is reactive. Chapter 7 Sigma Bonds of Ethylene Chapter 7 Orbital Description Sigma bonds around the double-bonded carbon are sp2 hybridized. Angles are approximately 120º and the molecular geometry is trigonal planar. Unhybridized p orbitals with one electron will overlap forming the double bond (pi bond) . Chapter 7 Bond Lengths and Angles sp2 hybrid orbitals have more s character than the sp3 hybrid orbitals. Pi overlap brings carbon atoms closer shortening the C—C bond from 1.54 Å in alkanes down to 1.33 Å in alkenes. Chapter 7 Pi Bonding in Ethylene The pi bond in ethylene is formed by overlap of the unhybridized p orbitals of the sp2 hybrid carbon atoms. Each carbon has one unpaired electron in the p orbital. This overlap requires the two ends of the molecule to be coplanar. Chapter 7 Cis-Trans Interconversion Cis and trans isomers cannot be interconverted. No rotation around the carbon—carbon bond is possible without breaking the pi bond (264 kJ/mole). Chapter 7 Elements of Unsaturation Unsaturation: A structural element that decreases the number of hydrogens in the molecule by two. Double bonds and rings are elements of unsaturation. To calculate: Find number of hydrogens if they were saturated, subtract the actual number of hydrogens, then divide by 2. Chapter 7 Example: Calculate the Unsaturations for a Compound with Formula C5H8. First calculate the number of hydrogen atoms for a saturated compound with five carbons: (2 x C) + 2 (2 x 5) + 2 = 12 Now subtract from this number the actual number of hydrogen atoms in the formula and divide by 2: 12 – 8 = 4 = 2 .