Topic 5: Alkenes pt1 Flashcards
Introduction
Alkenes= Carbon- carbon double bonds
Alkenes are also called OLEFINS… meaning “oil-forming gas”
The functional group of alkenes is the carbon-carbon double bond, which gives this group its reactivity.
Orbital Description
Sigma bonds around the double-bonded carbon= sp2 hybridized
Angles= 120° -» Trigonal planar
Unhybridized p orbitals with one electron will overlap, forming the double bond (pi bonds)
General Molecular Formula for Alkenes
π bond introduces… reduces the H content by 2
CH3CH2CH2CH=CH2 -> CnH2(n)
General Molecular Formula for Alkenes pt2
Generalization: The molecular formula for a hydrocarbon is CnH2(n)-2 hydrogens for every π bond/or ring
Nomenclature of Alkenes
IUPAC names… based on the alkane with “-ane” replaced by “-ene”
Common name:
Ethylene or Propylene
Systematic name:
Ethene or Propene or Cyclopentene
Name the Alkene (Step 1)
- Find the longest, continuous C chain that contains the double bond. (Use it to determine the base name)
Drop the -ane replace to “-ene”
Because the longest chain with the double bond has 6 carbons
Base name is: Hexene
Name the Alkene (Step 2)
- Identify the substituent branches
There are 2 substituents:
One of them have 1 C chain= Methyl
the other one is a 2 C chain = ethyl
Name the Alkene (Step 3)
3.Number the chain and substituents
A) Determine the end closest to the double bond
B)Then assign # to each substituent based on the # of the main chain C it is attached to.
Name the Alkene (Step 4)
- Write the name in the following order:
A) Substitutents # first alphabetical substituting… name of first alphabetical substituting.
B) Repeat for other substituents
C) # of first C in double bond- name of the chain.
IUPAC Rules for Alkene Nomenclature (Cyclic)
- In cyclic compounds, a # is not needed to denote the position of the functional group.
-The double bond is assumed to be between carbons 1 & 2.
Important things to remember
-2 groups containing double bonds that are used as names for substituents are vinyl group and the allyl group.
Ex:
Vinyl group: CH2=CH-Cl
IUPAC Name:Chloroethene
Common name: Vinyl Chloride
Allyl Group: CH2=CH-CH2-Br
IUPAC Name: 3-bromopropene
Common name: Allyl bromide
Important things to remember pt2
Sp2 carbons of alkene are called vinylic.
-C=Ch: Vinylic carbons
RCH2-X=X-CH2R: Allylic carbons
An sp3 adjacent carbon is allylic