Ch. 9 - Alkenes and AlkynesWorksheetSee all chapters
All Chapters
Ch. 1 - A Review of General Chemistry
Ch. 2 - Molecular Representations
Ch. 3 - Acids and Bases
Ch. 4 - Alkanes and Cycloalkanes
Ch. 5 - Chirality
Ch. 6 - Thermodynamics and Kinetics
Ch. 7 - Substitution Reactions
Ch. 8 - Elimination Reactions
Ch. 9 - Alkenes and Alkynes
Ch. 10 - Addition Reactions
Ch. 11 - Radical Reactions
Ch. 12 - Alcohols, Ethers, Epoxides and Thiols
Ch. 13 - Alcohols and Carbonyl Compounds
Ch. 14 - Synthetic Techniques
Ch. 15 - Analytical Techniques: IR, NMR, Mass Spect
Ch. 16 - Conjugated Systems
Ch. 17 - Aromaticity
Ch. 18 - Reactions of Aromatics: EAS and Beyond
Ch. 19 - Aldehydes and Ketones: Nucleophilic Addition
Ch. 20 - Carboxylic Acid Derivatives: NAS
Ch. 21 - Enolate Chemistry: Reactions at the Alpha-Carbon
Ch. 22 - Condensation Chemistry
Ch. 23 - Amines
Ch. 24 - Carbohydrates
Ch. 25 - Phenols
Ch. 26 - Amino Acids, Peptides, and Proteins

Now it’s time to introduce some of the most important nucleophiles in all of organic chemistry, alkynides

Concept #1: Understanding how to convert terminal alkynes to alkynides.

Recall that most hydrocarbons are terrible acids, having pKas from 40-50. However, terminal alkynes (alkynes with a hydrogen) are uniquely acidic due to the hybridization effect, having a pKa of 25.

This means they can be easily deprotonated using a strong base (typically NaH or NaNH2). 

The resulting conjugate base is known as a sodium alkynide, and these are often used to lengthen carbon chains to through SN2 reactions.

  • For now, this will be the only way to increase the number of carbons in your product.

Let's take a look at the mechanism of akynide synthesis.

Concept #2: The mechanism of akynide synthesis.

Beware: You can only use this reaction with primary alkyl halides. Secondary alkyl halides will favor E2!

Let's put it all together!

Concept #3: Using double dehydrohalogenation to perform alkynide synthesis. 

Example #1: Predict the final product of the following reaction sequence.  

Additional Problems
Predict the product for the reaction below.
Identify the statement as either True (A) False (B) Sodium hydroxide is a strong base and can be used to deprotonate terminal alkynes in a 100% yield.
Provide the mechanism for the multi step process, by which an alkene is converted to a terminal alkyne. Show all flow of electrons, formal charges and account for stereo- & regiochemistry.
Select the best base to quantitatively remove a proton from acetylene. a) NaNH2 b) NH3 c) NaOH d) NaOCH2CH3
Predict the product(s) for the following reaction.
You need to show how the starting material can be converted into the product(s) shown. You may use any reactions we have learned provided that the product(s) you draw for each step is/are the predominant one(s). Show all the reagents you need. Show each molecule synthesized along the way and be sure to pay attention to the regiochemistry and stereochemistry preferences for each reaction. You must draw all stereoisomers formed, and use wedges and dashes to indicate chirality at each chiral center. Write racemic when appropriate.
Give all possible product/products and designate stereoselectivity &/or regioselectivity by using wedges and dashes.   
Predict the product:  
Predict the organic product(s) of the following reaction. When appropriate, be sure to indicate stereochemistry. If more than one product is formed be sure to indicate the major product, if stereoisomers are produced in the reaction be sure to indicate the relationship between them. Draw the answer in skeletal form.
Identify the alkyl halide that would produce 1-cyclohexyl-1-butyne.     
What is the major organic product of the following reaction?
Click on the drawing box above to activate the MarvinSketch drawing tool and then draw your answer to this question. If there is no reaction, then check the "no reaction: box below. no reaction
What is the starting material in the following reaction? (a) II (b) I (c) III (d) IV
Draw an alkyl iodide that could be used to make the alkyne shown. 
Unlimited Draw the major product of the following reaction. If two organic products are obtained, draw them both. 
Write the structural formula and name of the organic product for the following reaction between an alkyne and an alkyl halide. (The alkyne group is shown, and should be entered, as "CC", without the triple bond
Provide the major organic product of the reaction below.
Draw the major organic product(s) of the following reaction.   
Draw the organic product(s) of the following reaction.