Study Set Content:
In the addition of HX to an alkene
- H attaches to the carbon with fewer alkyl substituents
- X attaches to the carbon with more alkyl substituents
Markovnikov’s Rule
R–C≡C–R
Alkynes
CnH2n-2
Alkynes
CnH2n
Alkenes
Each triple bond reduces the number of
hydrogen atoms by
4
Hydrocarbon molecules with one or more triple bonds are called
Alkynes
alkynes; they make up another series of
Unsaturated hydrocarbons
Two carbon atoms joined by a triple bond are bound together by
σ bond and two π bonds.
Linear carbon chains of sp-hybridized carbon atoms. The sp-hybridized carbons involved in the triple bond have bond angles of 180°, giving these types of bonds a linear, rod-like shape.
Polyynes
The simplest member of the alkyne series is
Ethyne
C2H2
ethyne
common name for ethyne
acetylene
Physical Properties:
of alkyne
Alkynes are nonpolar, unsaturated hydrocarbons with physical properties similar to alkanes and alkenes. Alkynes dissolve in organic solvents, have slight solubility in polar solvents, and are insoluble in water. Compared to alkanes and alkenes, alkynes have slightly higher boiling points.
- Alkyne is more reactive than alkanes. The existence of a triple bond which is owned alkyne allow the addition reactions, polymerization, substitution and combustion.
Uses of Alkyne:
- Acetylene, the simplest alkyne, is used in torches to generate temperatures of around 3,000 degrees Celsius to weld metal by generating oxy-acetylene welding.
- It is also used as a starting material in the synthesis processes used to make polymers, and as a solvent.
- Alkynes are generally used as the starting materials for the manufacture of a large number of organic compounds of industrial importance such as, chloroprene, vinyl chloride etc.
- Alkynes are also highly important parts of some antitumor agents.
Chemical properties
IUPAC Rules for Alkyne Nomenclature
- The yne suffix (ending) indicates an alkyne or cycloalkane.
- The longest chain chosen for the root name must include both carbon atoms of the triple bond.
- The root chain must be numbered from the end nearest a triple bond carbon atom. If the triple bond is in the center of the chain, the nearest substituent rule is used to determine the end where numbering starts.
- The smaller of the two numbers designating the carbon atoms of the triple bond is used as the triple bond locator.
- If several multiple bonds are present, each must be assigned a locator number. Double bonds precede triple bonds in the IUPAC name, but the chain is numbered from the end nearest a multiple bond, regardless of its nature.
- Because the triple bond is linear, it can only be accommodated in rings larger than ten carbons. In simple cycloalkanes the triple bond carbons are assigned ring locations #1 and #2. Which of the two is #1 may be determined by the nearest substituent rule.
- Substituent groups containing triple bonds are:
HC=C- Ethynyl group
HC=C-CH2- Propargyl group
Naming of alkynes
- General hydrocarbon rules apply
- Suffix -yne indicates an alkyne
- Number of the first alkyne carbon in the chain is used to indicate the position of the triple bond
Alkynyl groups are also possible
Alkynyl groups are also possible
- Addition reactions of electrophiles with alkynes are similar to those with alkenes
- Regiochemistry according to Markovnikov's rule
- Addition of HX and X2
Addition products are formed when bromine and chlorine are added, resulting in trans stereochemistry
- Addition of HX and X2
catalyzed hydration of alkynes
Mercury
