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CHEM152Lnotes(6-30-09)

CHEM152Lnotes(6-30-09) - CHEM 152L Summer 2009 Alkynes...

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CHEM 152L Summer 2009 Alkynes – hydrocarbons that contain triple bond General molecular formula is C n H 2n-2 . Very few naturally occurring alkynes – Examples O capillin O OH H ichthyothereol capillin – fungicidal activity ichthyothereol – convulsant Few drugs that contain alkyne functionality – O H 2 N parsalmide N pargyline CH 3 OH C CH H 3 CO mestranol
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CHEM 152L Summer 2009 Probably the most common alkyne is acetylene - HC CH - used in welding, when burned it produces a flame that is high enough temperature that it can melt iron and steel. Nomenclature of alkynes is very similar to that of alkanes, alkenes, “ane” is replace with “yne” Find longest continuous chain of carbons CONTAINING the functionality – number from end that gives the alkyne the lowest number possible. EX. Reactivity considerations of alkynes – Look at the multiple bond in the case of the alkyne, this is an area of significant electron density, as a result we can think of the alkyne as a nucleophile, so when we react the alkyne with something like a HCl, we see a very similar reaction to that of an alkene. + HCl H 3 C Cl H CH 3 MECH – The same electrophilic reagents that add to alkenes will add to alkynes and as with alkenes there are regioselective consequences. A terminal alkyne will show Markovnikov addition. But there is another complication with electrophilic addition to an alkyne, that is the fact that the initial addition yields an alkene and we know that the alkene can undergo electrophilic addition.
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