Chapter9 - Organic Chemistry CHE 275 Chapter 9 Alkynes...

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Organic Chemistry CHE 275 Chapter 9 Alkynes
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Industrial preparation of acetylene is by dehydrogenation of ethylene CH 3 CH 3 800°C 1150°C cost of energy makes acetylene a more expensive industrial chemical than ethylene H 2 C CH 2 H 2 C CH 2 HC CH H 2 + H 2 + Acetylene
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Naturally Occurring Alkynes C(CH 2 ) 4 COH CH 3 (CH 2 ) 10 C O Tariric acid: occurs in seed of a Guatemalan plant Some alkynes occur naturally. For example,
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HC CH Acetylene and ethyne are both acceptable IUPAC names for Higher alkynes are named in much the same way as alkenes except using an - yne suffix instead of - ene . HC CCH 3 Propyne HC CCH 2 CH 3 1-Butyne or But-1-yne (CH 3 ) 3 CC CCH 3 4,4-Dimethyl-2-pentyne or 4,4-Dimethylpent-2-yne Nomenclature
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The physical properties of alkynes are similar to those of alkanes and alkenes. Physical Properties of Alkynes
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linear geometry for acetylene C C H H 120 pm 106 pm 106 pm C C CH 3 H 121 pm 146 pm 106 pm Structure
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Cyclononyne is the smallest cycloalkyne stable enough to be stored at room temperature for a reasonable length of time. Cyclooctyne polymerizes on standing. Cycloalkynes C C
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2 s 2 p 2 sp Mix together (hybridize) the 2s orbital and one of the three 2p orbitals 2 p sp Hybridization in Acetylene
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2 sp Mix together (hybridize) the 2s orbital and one of the three 2p orbitals 2 p Each carbon has two half-filled sp orbitals available to form σ bonds. sp Hybridization in Acetylene
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Each carbon is connected to a hydrogen by a σ bond. The two carbons are connected to each other by a σ bond and two π bonds. σ Bonds in Acetylene
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One of the two π bonds in acetylene is shown here. The second π bond is at right angles to the first. π Bonds in Acetylene
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This is the second of the two π bonds in acetylene. π Bonds in Acetylene
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The region of highest negative charge lies above and below the molecular plane in ethylene . Electrostatic Potential in Acetylene The region of highest negative charge encircles the molecule around its center in acetylene .
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C—C distance C—H distance H—C—C angles C—C BDE C—H BDE % s character p K a 153 pm 111 pm 111.0° 368 kJ/mol 410 kJ/mol sp 3 25% 62 134 pm 110 pm 121.4° 611 kJ/mol 452 kJ/mol sp 2 33% 45 120 pm 106 pm 180° 820 kJ/mol 536 kJ/mol sp 50% 26 hybridization of C Ethane Ethylene Acetylene Comparison of Ethane, Ethylene, and Acetylene
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H C C Acidity of Acetylene and Terminal Alkynes
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In general, hydrocarbons are exceedingly weak acids Compound p K a HF 3.2 H 2 O 15.7 NH 3 36 45 CH 4 60 H 2 C CH 2 Acidity of Hydrocarbons
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as weak as alkanes or alkenes. Compound
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This note was uploaded on 10/17/2011 for the course CHE 275 taught by Professor Totah during the Fall '08 term at Syracuse.

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Chapter9 - Organic Chemistry CHE 275 Chapter 9 Alkynes...

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