Learning Guide for Chapter 13 - Alkynes I. Introduction to Alkynes - p 1 II. Natural ccurrence and Uses of Alkynes - p 5 III. Physical Properties of Alkynes - p 7 IV. Spectroscopy of Alkynes - p 7 V. Nomenclature of Alkynes - p 8 VI. Acid-base Properties of Alkynes - p 12 VII. Synthesis of Alkynes by Elimination - p 14 VIII. Reduction of Alkynes to Form Alkenes and Alkanes - p 15 I. Addition of and 2 to Alkynes - p 17. ydration of Alkynes - p 18 I. xidation of Alkynes - p 20 I. Introduction to Alkynes Classifying Alkynes Which of these is an? What is the other one called? Which of these is a terminal? Which is an internal? Alkenes could also be labeled this way, but they aren't. Why not?
ybridization and bond formation LG Ch 13 p 2 What hybridization do each of the carbons in acetylene have? C C What kind of molecular orbital forms each bond? C C Where do each of the bonds come from? C- bond C-C! bond C-C " bonds C C What orientation will the pi bonds have to each other? ow do triple bonds compare to double and single bonds in length? C C 2 C C 2 3 C C 3 Geometry What geometry do carbons in triple bonds have? Draw a 6 carbon with the triple bond on the end. Then draw a 6 carbon with the in the middle. ow big does a ring have to before it can contain a triple bond (and be stable)?
Stereochemistry LG Ch 13 p 3 Can the carbon in a triple bond be a stereocenter? Can s be chiral? Molecular formula ow many units of unsaturation does a triple bond have? What is the molecular formula for a simple? What would be the formula of an with 10 carbons? What would be the formula of a cyclic with 10 carbons? Stabilization Which is more stable, an internal or a terminal? Why?
LG Ch 13 p 4 Reactivity Where are the two places that s can react? ow can a terminal react with a base? base ow can an react with an acid? With an electrophile? -base E Which is more reactive, an alkene or an? ow is the product of an reaction different from the product of an alkene reaction? alkene: Cl : Cl
II. Natural ccurrences and Uses of Alkynes LG Ch 13 p 5 Alkynes are rarely found in nature. What is one exception? Unsaturated compounds with carbon-carbon triple bonds have been found. ow many are known? What do they often have in common? ere are some examples: capicillin cicutoxin tariric acid hystrionicotoxin Unsaturated compounds with carbon-carbon triple bonds have also been isolated or synthesized for use as drugs. ere are some examples: ethynyl estradiol parsalmide N 2 N
LG Ch 13 p 6 pargyline dynemicin A N N What is the most useful in industry? ow is it made? ow is it stored? What happens when it burns? What is polyacetylene? What is it used for?
III. Physical Properties of Alkynes LG Ch 13 p 7 Give the following properties of s: polarity water solubility density melting and boiling points flammability storage issues odor state of matter IV. Spectroscopy of Alkynes IR Spectroscopy What two bonds do s have that alkanes do not? ow do the IR spectra of terminal s differ from those of internal s?
ow does the carbon-carbon triple bond band compare to a double bond band? LG Ch 13 p 8 ow does the triple bond in an compare to the triple bond in a nitrile? ow does the C- on an compare to the C- on an alkene? 1 NMR Spectroscopy Where do 's on terminal s appear? Is the on a terminal always a singlet? 13 C NMR Spectroscopy Where do C's in the triple bond of an appear? Common names V. Nomenclature of Alkynes Give common names of the following compounds.
IUPAC names What steps should you follow when naming an? LG Ch 13 p 9 1. 2. 3. 4. What are the priorities for choosing the principle chain? ow are the names formed? What are the priorities for numbering the principle chain?
LG Ch 13 p 10 ow do you name a substituent containing a carbon-carbon triple bond? Where do you number a substituent from?
Name the following compounds. LG Ch 13 p 11 Cl Draw the following compounds, using the correct geometry! 5-methyl-3-octyne cyclohexylacetylene 3-ethynyl-1-cyclohexene
VI. Acid-base Properties of Alkynes LG Ch 13 p 12 ow does the electronegativity of an atom affect the acidity of a attached to it? ow acidic would you expect a attached to a C to be? Why are s more acidic than alkenes or alkanes? What is the conjugate base of an called? + Na base What kind of base would be required to successfully react with an? What would happen if an acetylide ion came in contact with an acid with a pka less than 26? pka 16 + Na ow do anions react? Na Br Na Br Which is more useful?
LG Ch 13 p 13 ow could an S N 2 reaction be used to synthesize 5-methyl-1-hexyne from acetylene? C C What alkyl halide would be needed to make the following s? ow many steps would be needed to make an internal from acetylene? C C Why can't you add both alkyl halides at the same time? What difficulties would you encounter in making the following s?
VII. Synthesis of Alkynes by Elimination LG Ch 13 p 14 When s can't be formed by a substitution reaction, what other method is available? substitution ow can elimination be used to make C=C? Br (C 3 ) 3 CK What is different about making a triple bond? NaN 2 NaN 2 Br Br Why is a stronger base needed? Why aren't cumulated dienes formed? When a terminal is formed, an addition step where water is added is necessary. Why is this? Br 2 eq NaN 2 Br ow can this reaction be used to make alkenes into s? 2 eq NaN 2 2. 2
VIII. Reduction of Alkynes to Form Alkenes and Alkanes LG Ch 13 p 15 What kinds of compounds can be formed when s undergo an addition reaction with hydrogen? When an is reacted with 2 and a metal catalyst, what kind of product results? 2, Pt/C Why can't we isolate the product of the first stage of this reaction? Why does the alkene intermediate have cis stereochemistry? ow can this reaction be used to determine the relative stability of terminal and internal s? 2, Pt/C 2, Pt/C ow could you use this reaction to synthesize an alkane chain?
What can you do to stop the reaction at the alkene? LG Ch 13 p 16 What advantage does this have over E2 reactions to make alkenes? What this can you tell about the reactivity of alkenes and s from this reaction? ow can a trans alkene be formed? ow is the Na here different from Na? Why can this be called a dissolving metal reaction? Where do the 's come from? What is the mechanism of this reaction? Na Na N N
Synthesize the following compounds from an. LG Ch 13 p 17 Addition of I. Addition of and 2 to Alkynes If Cl, Br, or I is added to an, what product will result? Br Br Which of these reactions demonstrates regioselectivity, and which side gets the halide? What will happen if an internal is not symmetrical? What will happen if a second equivalent of is added?
What happens if there is peroxide present in an Br addition? LG Ch 13 p 18 Br RR Addition of 2 What products are formed when one or two equivalents of Br 2 are added to an? Br 2 2 eq Br 2 Acid- and mercury-catalyzed hydration. ydration of Alkynes What reagents are required to add water across a carbon-carbon triple bond? What kind of product results? What happens to it? Which side is favored on a terminal? 2 S 4, 2 gs 4 What will happen if an internal is not symmetrical? 2 S 4, 2 g(ac) 2
ydroboration-oxidation of s LG Ch 13 p 19 What product results when an is treated with a borane reagent? 1. B 3 -TF 2. 2 2, - What complication could occur? ow do we prevent this? B B What regioselectivity is observed when an is treated with a borane reagent? 1. disiamylborane 2. 2 2, - ow could the following compounds be synthesized from an?
I. xidation of Alkynes LG Ch 13 p 20 What happens when an reacts with KMn 4? 2 eq KMn 4 2 What happens when an reacts with ozone? 3 2 Match the following reactions and products: KMn 4 2, Na 2 eq KMn 4 2, Na 1. g(ac) 2, 2 2. NaB 4 1. B 3 -TF 2. 2 2, Na 2 S 4, 2 g(ac)2 1. dicyclohexylborane 2. 2 2, Na
Synthesis of s Summary of reactions LG Ch 13 p 21 acetylene terminal C C NaN 2 C 3 Br terminal internal NaN 2 C 3 Br vicinal dihalide NaN 2 or K, 200 o C C C geminal dihalide NaN 2 or K, 200 o C C C Reactions of s alkane 2 Pd/C cis alkene 2 Lindlar trans alkene Na N 3 vinyl halide or geminal dihalide vicinal vinyl dihalide or tetrahalide 2 2 ketone g(ac) 2 2 S 4, 2 aldehyde 1. disiamyl borane 2. 2 2, Na diketone KMn 4 2 two carboxylic acids 3 2 2