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CHAPTER 11: ALKYNES

ALKYNE INTRODUCTORY TOPICS

EXAMPLES

DH˚ per mol

reactant (kcal/mol)

Adj. DH˚ per mol

product (kcal/mol)

-373 / 5 mol product

-75

-337 / 4 mol product

-84

-317 / 3 mol product

-106

H3C CH3 + 7/2 O2

2 CO2 3 H2O+

H2C CH2 + 3 O2

2 CO2 2 H2O+

HC CH + 5/2 O22 CO2 1 H2O+

C CH H

AcetyleneHot burning fuel

Welding

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ALYKNE NAMING

1.   Number so first carbon of the triple bond is the lowest # possible.

2.   When alkyne + alcohol are in the same molecule, the name is “#-alkyn-#-ol.” The alcohol is given the lower number.

“Synthesis of Anthropomorphic Molecules: The NanoPutians” Tour, J., J. Org. Chem, 2003, 68, 8750-8766

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1H NMR SPECTRA OF ALKYNES

CHEMICAL SHIFT

Alkene H: Alkyne H:

TERMINAL ALKYNE SPLITTING

Zoom in of peak at 2.1 ppm

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ALKYNE REACTIONS

BOND ENERGIES

Bond Type(s) kcal/mol

C-C s 88

C=C 152

200

GENERAL REACTION PATTERN

ADDITION OF X2

GENERAL PATTERN

MECHANISM

C C CH3H3CBr2

CH2Cl2

X= Cl, Br

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ADDITION OF HX

GENERAL PATTERN

MECHANISM

ADDITION TO ASYMMETRIC ALKYNES

C C CH3H3CHBr

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TERMINAL ALKYNE ACIDITY

Compound

pKa

ACETYLIDE REACTIONS

ACID-BASE REACTION

SUBSEQUENT REACTIONS

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SUMMARY PROBLEMS Synthesizing alkynes from acetylene:

Synthesize this alkyne from a terminal alkyne:

Give the major organic product.