Chapter 7 Alkenes and Alkynes 1 Flashcards
What are the simplest alkene and alkyne possible?
Simplest alkene: Ethylene
Simplest Alkyne: Acetylene
What is the structure in the image?
Ethylene
The simplest alkene
What is the molecule in the image?
Propylene OR
1-propene (prop-1-ene)
What is the relationship between the two molecules/
Diastereomers
What is the difference between the E and Z stereochemistry?
- E: entegegan = opposite
- highest substituents are on opposite sides
- Z: zusammen = Same
- highest substituents are on the same side
Are the compounds the same?
No, they are diastereomers and we can differentiate them by using the E and Z nomenclature
What is the functional group in the image?
Vinyl group
eg:
Vinyl chloride
(1-chloroethene)
What is the functional group in the image?
Provide an example of a compound with the functional group
CH3CH=CH−X
Allyl group or “Propenyl Group”
Eg
Allyl chloride
(3-chloropropene)
Cl—C—C=C
What is the functional group in the image?
Provide an example of a compound with the functional group
Benzyl group
eg: Benzyl bromide
6-member benzene with CH2
What is the functional group in the image?
Provide an example of a compound with the functional group
Phenyl group
eg: Phenyl bromide “bromobenzene”
What are the four naming rules for alkynes?
- Find longest chain w/ max number of multiple bonds
- Number from end to give 1st multiply bonded position the lowest number
- Drop “ane” and add “yne”
- For multiple triple bonds, drop the ne and add diyne, triyne etc
What is the compound in the image?
Ethyne
“Acetylene”
What are the names of the three compounds?
Are they related?
Propyne
1-butyne
2-butyne
- 1-butyne and 2-butyne are structural isomers
What is the name of the compound?
2,4 - Octadiyne
What is the name of the compound?
- 13 Carbons = trideca
- triple bond (triyne) on 5, 7, 9
- 3 double bonds (triene) on 1, 3, 11
- 3=4 E (opposite)
- 11=12 E (opposite)
= 3E,11E-trideca-1,3,11-triene-5,7,9-triyne
What is the relative polarity of alkanes, alkenes and alkynes?
Alkynes > Alkenes > Alkanes
most polar -> least polar
What is the relative acidity of Alkanes, alkenes and alkynes?
Least acidic -> most acidic
Alkane < Alkene < Alkynes
Least polar -> Most polar
What three properties are higher in alkynes than in alkenes and alkanes?
Alkynes have a higher boiling point, melting point, and density
What is Hydrogenation?
- “add’n of hydrogen to an alkene in presence of metal catalysts to produce alkanes”
- Reaction from the addition of H2
- Stereospecific
- cis or syn add’n
- Metal catalysts
How do catalysts increase the rate of reaction?
Provide a lower energy pathway.
- are not permanently converted to other products
What are the relative stabilities of alkenes?
(1-butene vs trans-2-butene vs cis-2-butene)
Trans is most stable and 1-butene (unsubstituted) is the least stable.
Trans-2-butene > Cis-2-butene > 1-butene
The ______ on a double bond, the more stable
The more substituents on a double bond, the more stable
Why are double bonds with more substituents more stable?
Carbons on a double bond have a partially positive charge which is stabilized by the e- donating effects of alkyl groups
hydrogens are less e- donating= less stable
Why are cis alkenes less stable than trans alkenes?
cis alkenes have methyl groups facing the same direction which causes unfavourable steric interactions = decreases stability
what is the compound in the image?
Fat:
- A triglyceride: triester of glycerol
- polyunsaturated (>1 double bond)
What is the reaction converting a polyunsaturated triglyceride into a saturated fat?
Hydrogenation of Polyunsaturated triglyceride:
- polyunsaturated triglyceride –(H2)/Ni–>
- removes double bonds
- saturated fat (triglyceride)
What is the compound in the picture?
Diacetyl
butter flavouring that add yellow colour to margarine
IUPAC = butanedione or butane-2,3-dione
Why do deuteriums add to the back of steroids in a hydrogenation rxn?
(deuteriums are isotope of Hydrogen 2H)
Because of steric hindrance of the nearby methyl group
Products: Two possible diastereomers depending on bottom or top addn
Bottom: equatorial isopropyl and axial methyl
Top: isopropyl and methyl are equatorial
Hydrogenation reaction requiring a metal catalyst and H2
What is halogenation?
Add’n of halogens across a double bond
Converts alkene to alkane
Halogenation of cyclopentene produces 1:1 racemate of trans-1,2-dibromocyclopentane enantiomers (RR; SS)
Requires:
Halogenation of cyclopentene requires Br2 and achiral solvent and produces:
Halogenation of 1,2-dimethylcyclopentene produces trans-1,2-Dibromo-1,2-dimethylcyclopentane
And requires: ____
Halogenation of 1,2-dimethylcyclopentene produces ____________
And requires: Br2
What is Markovnikov’s Rule?
In an addition reaction, the positive end of an A-B system (eg I-Cl) adds to the least substituted end of the double bond to make the more stable carbocation
Which is faster, intermolecular or intramolecular reactions?
Intramolecular reactions are faster: within the same molecule
Therefore, intramolecular almost always beats intermolecular reactions
What is Zaitsev’s rule?
Formation of the more substituted alkene is favored with a small base.
- if we use a small base (eg ethoxide or hydroxide) the major product of the rxn will be the more highly substituted alkene (more stable alkene)
Whenever an elimination occurs to give the more stable, more highly substituted alkene, chemists say that the elimination follows _______
Whenever an elimination occurs to give the more stable, more highly substituted alkene, chemists say that the elimination follows Zaitsev’s rule
What is kinetic control of product formation?
The preferential formation of one product b/c the free energy of activation leading to its formation is lower than that for another product, and therefore the rate of its formation faster
Carrying out dehydrohalogenations with a bulky base such as potassium tert-butoxide (t-BuOK) in tert-butyl alcohol (t-BuOH) favours the formation of:
Carrying out dehydrohalogenations with a bulky base such as potassium tert-butoxide (t-BuOK) in tert-butyl alcohol (t-BuOH) favours the formation of the less substituted alkene
When an elimination yields the less substituted alkene, we say that it follows the ________ rule
When an elimination yields the less substituted alkene, we say that it follows the hofmann rule
