Chemical Reactions and Organic Compounds - Prof. Shawn Hitchcock, Study notes of Organic Chemistry

Download Chemical Reactions and Organic Compounds - Prof. Shawn Hitchcock and more Study notes Organic Chemistry in PDF only on Docsity! © 2008 Assoc. Prof. S. R. Hitchcock, Department of Chemistry, Illinois State University, Normal, IL 61790 1 Illinois State University Dr. Hitchcock, Department of Chemistry, Illinois State University, Normal, IL 61790-4160 Chapter 11: The Chemistry of the Alkenes 1. Provide reasonable IUPAC names for the following molecules. (Read section 11.1 in the text for help with these problems. Do problems 11.1-11.4 and 11.26 and 11.27.) C(CH3)3 OCH3 OH CH3 Br OH CH3 H3C Br Cl Cl 3-tert-butyl-1-cyclohexene or 3-tert-butylcyclohexene 1-methoxy-1-cyclobutene 1-methoxycyclohexene 157 5-ethyl-7-methyl-1-octene cis-2-chloro-3-isopropyl-4-octene cis-2-chloro-3-(1-methylethyl)-4-octene 1 1 2-methyl-6-hepten-3-ol trans-3-hepten-2-ol (Z)-3-bromo-4-methyl-3-heptene (E)-3-bromo-2-chloro-2-octene © 2008 Assoc. Prof. S. R. Hitchcock, Department of Chemistry, Illinois State University, Normal, IL 61790 2 2. Provide a bond description for ethene. In addition, describe the bond angles and overall geometry. Describe the length of the bond in ethene vs. ethane. Which bond is stronger? (Read section 11.2 for help with this section and do problem 11.56.) σ[C(sp2)-C(sp2)] + σ *(empty orbital) and π[C(p)-C(p)] + π * (empty orbital) trigonal planar, 120o bond angle; shorter and stronger than the carbon-carbon bond in ethane. 3. Based on the information that you have provided, would you expect cyclopropene to be a stable molecule? Provide a rationale for your answer. (Read section 11.2 for help with this section.) No. The required bond angle is 120o for an alkene and cyclopropene has an alkene with a bond angle of 60o. 4. What is the stereochemistry term used to describe the relationship between the cis- and trans- molecules below? Provide a concrete definition for this term. (Read section 11.2 for help with this section.) H3C H H CH2CH3 H H H3C CH2CH3 and These compounds are diastereomers, stereoisomers that cannot be related by a mirror plane. 5. Provide the products of the following transformations. Assume that all hydrogenations occur at near 1 atmosphere of pressure. If there is no reaction, then write NR. (Please see section 11.9 for more information concerning the hydrogenation of alkenes. Do problems 11.18, 11.19, 11.45 and 11.46.) H2, Pd EtOH CH2CH3 H2, Pt EtOH H2, Pt EtOH CH2CH=CH2 H2, Pt EtOH OCH3 OH OCH3H H CH2CH3 H H CH2CH2CH3 OH No reaction. The pi-electrons are delocalized and do not respond to hydrogen gas expsosure at atmospheric pressure. © 2008 Assoc. Prof. S. R. Hitchcock, Department of Chemistry, Illinois State University, Normal, IL 61790 5 11. Complete the following reactions. Indicate which product is the major product and which is the minor. State the pathway of elimination, either Zaitsev or Hoffmann. What is the dominant pathway in each case? (Complete problem 11.57 in the text book for extra work.) OTs OH Br CH3 NaOCH 3 in CH 3OH LiOCH 3 in CH 3OH CH2CH3 Cl CH2CH2I KOEt in EtOH LiOCH 2CH3 CH3CH2OH EtOH = CH3CH2OH NaOCH 3 in CH 3OH Br KOC(CH 3)3 (CH3)3COH Br 100 oC 100 oC 100 oC 100 oC 100 oC 100 oC 100 oC KOC(CH 3)3 (CH3)3COH TsO = tosylate leaving group CH3 CH2 major minor cis + trans (minor)major Zaitsev Hofmann CH2CH3 CH2CH3 major minorZaitsev No reaction. There is no leaving group to undergo the elimination process. Hydroxide is not a suitable leaving group for the E2 process. The alcohol would only deprotonate. major Hofmann Zaitsev CH2 major minor minor CH3 This reaction would not be classified as either Zaitsev or Hofmann as the alkene generated is the only possible alkene. © 2008 Assoc. Prof. S. R. Hitchcock, Department of Chemistry, Illinois State University, Normal, IL 61790 6 12. Provide the major and minor alkenes from the following reactions and circle the major alkene. Indicate the level of substitution for this alkene. What is the dominant reaction mechanism for all of these reactions? (Do problem 11.22 for a better understanding of these reactions. By what mechanism do these reactions operate?) H3PO4 heat OH Et H3PO4 heat OH H2SO4 heat OH OH H3PO4 heat H2SO4 heat OH H2SO4 heat H3PO4 heat OH CH3 Et Et The most stable alkene is always the dominant product under conditions involving strong acid. The elimination of secondary and tertiary alcohols involves carbocations! The unwritten by-products for each reaction is water. + There is no reaction in terms of forming a new alkene. There is no suitable β-hydrogen for straightforward removal. trans and cis-isomers + trans and cis-isomers This is the exclusive alkene product for this reaction. CH3 CH2major minor major minor major minor No reaction. There is no leaving group. Cyclopentane will not react under these conditions. trisub. disub. disub. monosub. monosub. disub. disub. tetrasub. + © 2008 Assoc. Prof. S. R. Hitchcock, Department of Chemistry, Illinois State University, Normal, IL 61790 7 13. Provide a mechanistic explanation for the following transformation. Identify nucleophiles and electrophiles. What is the name given to key process that leads into the alkene product? O H2SO4 heat CH3 CH3 CH3 CH3 H H nucleophile electrophile OCH3 CH3 HH CH3 CH3 H This hydrogen was always there. It did not appear from nowhere. H The major transformation is a carbocation. CH3 CH3 H H H H O HH E1 elimination pathway