Lecture_19-20

Lecture_19-20 - Lecture 19&20 Chapter 6: ...

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Unformatted text preview: Lecture 19&20 Chapter 6: The Reac5ons of Alkynes Mul5ple Func5onal Groups  Longest chain to include both suffixes What is the IUPAC name for the following alkyne?  A) 5- Bromo- 2- heptyne  B) 3- Bromo- 5- heptyne  C) 2- Bromo- 2- methyl- 4- hexyne  D) 5- Bromo- 5,5- dimethylhexyne  E) 5- Bromo- 5- methyl- 2- hexyne What is the IUPAC name for the following alkyne?  A) 5- Bromo- 2- heptyne  B) 3- Bromo- 5- heptyne  C) 2- Bromo- 2- methyl- 4- hexyne  D) 5- Bromo- 5,5- dimethylhexyne  E) 5- Bromo- 5- methyl- 2- hexyne What is the common name for the following alkyne?  A) neohexyne  B) trimethylpropyne  C) trimethylacetylene  D) tert- butylacetylene  E) isopropylacetylene What is the common name for the following alkyne?  A) neohexyne  B) trimethylpropyne  C) trimethylacetylene  D) tert- butylacetylene  E) isopropylacetylene Which is the systema5c name for the following compound? A.  B.  C.  D.  E.  3-ethynyl-1-hexene 3-ethenyl-1-hexyne 3-propyl-4-penten-1-yne 3-propyl-1-penten-4-yne 3-propyl-1,4-pentenyne Which is the systema5c name for the following compound? A.  B.  C.  D.  E.  3-ethynyl-1-hexene 3-ethenyl-1-hexyne 3-propyl-4-penten-1-yne 3-propyl-1-penten-4-yne 3-propyl-1,4-pentenyne The alkene has higher priority than the alkyne, if the two multiple bonds are equal distance from the end. Both functional groups should be included in the longest chain. Physical Proper5es of Unsaturated Hydrocarbons  RelaDvely non- polar & less dense than water  BP increases with molecular weight Structure of Alkynes Alkyne Reac5vity  Alkynes are nucleophiles too –  HBr addiDon to 2- butyne Alkyne Reac5vity  Is an alkyne more or less reacDve than an alkene? Alkyne Reac5vity  Vinylic CarbocaDons are less stable than 2° –  sp carbon is more electronegaDve than sp2 –  HyperconjugaDon is inneffecDve Addi5on of HX and X2 to Alkynes  AddiDon of HBr to 1- butyne –  2 possible carbocaDon intermediates…  ReacDon stops at alkene with 1 equivalent –  But didn’t we say alkene was more reacDve? –  Yea, but halo- subsDtuted alkene is more stable Addi5on Reac5ons  If excess HBr used…geminal dihalide is formed Stereoselec5vity in HX Addi5ons? Addi5on Reac5ons  HCl (excess) added to 2- hexyne:  HCl (excess) added to 3- hexyne Addi5on of Water  Remember addiDon of water to 1- butene?  AddiDon of water to 2- butyne: Tautomeriza5on  Keto- enol tautomerizaDon Making Ketones  Symmetrical internal alkynes give same ketone  Unsymmetrical ones give different ketones Making Ketones  Terminal alkynes less reacDve –  Need HgSO4 as a catalyst Hydrobora5on- Oxida5on  Only add 1/3 equiv BH3 to get the enol –  2- butyne hydroboraDon- oxidaDon…  Terminal alkyne gives an aldehyde: Addi5on of Hydrogen  We saw that metal/H2 reduced alkenes –  Difficult to stop at alkene from an alkyne •  Lindlar’s Catalyst (Pd on CaCO3 + Pb + quinoline) •  Gives syn addiDon of H2 and stops at alkene Trans Alkenes from Alkynes  Dissolving sodium in liquid ammonia @ - 78⁰C –  2- butyne gives trans- 2- butene Stability of Vinylic Anion  It’s all about steric hinderance Acidity of Terminal Alkynes  HybridizaDon of carbon affects acidity due to –  ElectronegaDvity sp > sp2 > sp3 –  Ethane pKa = 60, ethene = 44, ethyne = 25 –  What if OH- was used as the base? Synthesis using Acetylide Ions  “AlkylaDon reacDon” –  1- pentyne and NaNH2, then ethyl bromide Designing a Synthesis  How would you make this from the starDng material indicated? Designing Syntheses Mul5- Step Synthesis ...
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