lec 13 - Organic Lecture Series CH 310/318 M LECTURE 13...

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Organic Lecture Series 1 CH 310/318 M LECTURE 13 Textbook Assignment: Chap. 7- Alkynes Today’s Topics: Alkenes Alkenes -finish; Alkynes intro finish; Alkynes intro Notice & Announcements: (HW 4 Posted) Organic Lecture Series 2 Reactions Reactions of Alkenes of Alkenes Chapter 6 Chapter 6
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Organic Lecture Series 3 • Most alkenes react with H 2 in the presence of a transition metal catalyst to give alkanes. – Commonly used catalysts are Pt, Pd, Ru, and Ni. – The process is called catalytic reduction catalytic reduction or, alternatively, catalytic hydrogenation catalytic hydrogenation. – Addition occurs with syn stereoselectivity. + H 2 Pd Cyclohexene Cyclohexane 25°C, 3 atm Reduction of Alkenes Reduction of Alkenes Organic Lecture Series 4 • Mechanism of catalytic hydrogenation. Reduction of Alkenes Reduction of Alkenes
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Organic Lecture Series 5 Δ Δ H H o of Hydrogenation of Hydrogenation CH 2 =CH 2 3 CH=CH 2 Name Structural Formula Δ [kJ (kcal)/mol] Ethylene Propene 1-Butene cis -2-Butene trans 2-Methyl-2-butene 2,3-D imethyl-2-butene -137 (-32.8) -126 (-30.1) -127 (-30.3) -120 (-28.6) -115 (-27.6) -113 (-26.9) -111 (-26.6) Organic Lecture Series 6 • Reduction of an alkene to an alkane is exothermic. – There is net conversion of one pi bond to two sigma bonds. Δ H o depends on the degree of substitution of the carbon atoms of the double bond. – The greater the substitution, the lower the value of Δ H° i.e. greater substitution is more stable Δ H o for a trans alkene is lower than that of an isomeric cis alkene. –A trans alkene is more stable than a cis alkene. Δ Δ H H o of Hydrogenation of Hydrogenation
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Organic Lecture Series 7 Alkynes Alkynes Chapter 7 Chapter 7 Organic Lecture Series 8 • IUPAC: use the infix - yn yn- to show the presence of a carbon-carbon triple bond. • Common names: prefix the substituents on the triple bond to the word “acetylene”. Common name: IUPAC name: Dimethylacetylene Vinylacetylene 2-Butyne 1-Buten-3-yne 1 1,6-Heptadiyne 3-Methyl-1-butyne 6,6-Dimethyl-3-heptyne 2 3 4 1 2 34 5 6 1 2 3 4 5 6 7 7 Nomenclature Nomenclature
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Organic Lecture Series 9 • Similar to alkanes and alkenes of comparable molecular weight and carbon skeleton. 0.766 174 -36 0.746 125 -79 0.716 71 -132 0.690 40 -90 0.691 27 -32 (a gas) 8 -126 (a gas) -23 -102 (a gas) -84 -81 Density at 20°C (g/mL) Boiling Point (°C) Melting Point (°C) Formula Name 1-Decyne 1-Octyne 1-Hexyne 1-Pentyne 2-Butyne 1-Butyne Propyne Ethyne HC CH CH 3 CC H 3 C CCH 3 3 (CH 2 ) 2 H 3 2 H 3 2 ) 3 H 3 2 ) 5 H 3 2 ) 7 H
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lec 13 - Organic Lecture Series CH 310/318 M LECTURE 13...

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