CHEM 2211 1nd Edition Lecture 24 Outline of Last Lecture I Nomenclature of alkynes II Reaction of alkynes Outline of Current Lecture I Reactions of alkynes cont Current Lecture Reactions of alkynes continued The addition of boron to alkynes hydroboration oxidation BH3 or R2BH in THF is added to the alkyne After the addition a second step takes place o Aqueous sodium hydroxide and hydrogen peroxide are added The final product of this reaction will be an enol o But an enol will readily rearrange into a ketone Reaction and mechanism H3 C CH3C CCH3 R2BH THF CH3 HO H2O2 H2O C C H H3 C B R R CH3 C C H OH Enol Mechanism for Enol to Ketone H3 C CH3 C C O CH3CH2CCH3 These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute H OH A base removes a proton from the enol A pie bond forms between oxygen and carbon as the pie bond between the two carbons breaks carbon picks up a proton from water o Breaking the statement above down HO comes in an takes the H off of OH in the enol This kicks the bonding electrons onto O Forming the before said pie bond The H that was taken by HO is then kicked back onto the C in the double bond making it a single bond The addition of Hydrogen to an Alkyne The addition of H to alkynes is called hydrogenation the reaction takes place in H2 over Pd C o this takes an alkyne all the way to an alkane it can be stop in alkene stage if poisoned with a metal catalyst o most common is the lindlar catalyst Reaction all the way to an alkane CH3CH2C CH H2 Pd C CH3CH2CH CH2 H2 Pd C CH3CH2CH2CH3 Alkyne Alkene Alkane The highlighted area is where the H is attaching to break the triple bond into a double and then into a single Reaction when stopped with a metal catalyst CH3CH2C CH H2 Lindlar catalyst CH3CH2CH CH2 The addition that stop in alkene stage can be syn or anti H H H3 C C C CH3CH2 H C C CH3 Syn with Lindlar catalyst H CH2CH3 Anti with Na or Li NH3 liquid 78C
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