Topic 5: Alkenes pt1

Question 1

Introduction

Answer 1

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.

Question 2

Orbital Description

Answer 2

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)

Question 3

General Molecular Formula for Alkenes

Answer 3

π bond introduces… reduces the H content by 2

CH3CH2CH2CH=CH2 -> CnH2(n)

Question 4

General Molecular Formula for Alkenes pt2

Answer 4

Generalization: The molecular formula for a hydrocarbon is CnH2(n)-2 hydrogens for every π bond/or ring

Question 5

Nomenclature of Alkenes

Answer 5

IUPAC names… based on the alkane with “-ane” replaced by “-ene”

Common name:
Ethylene or Propylene

Systematic name:
Ethene or Propene or Cyclopentene

Question 6

Name the Alkene (Step 1)

Answer 6

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

Question 7

Name the Alkene (Step 2)

Answer 7

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

Question 8

Name the Alkene (Step 3)

Answer 8

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.

Question 9

Name the Alkene (Step 4)

Answer 9

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.

Question 10

IUPAC Rules for Alkene Nomenclature (Cyclic)

Answer 10

5. 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.

Question 11

Important things to remember

Answer 11

-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

Question 12

Important things to remember pt2

Answer 12

Sp2 carbons of alkene are called vinylic.
-C=Ch: Vinylic carbons
RCH2-X=X-CH2R: Allylic carbons

An sp3 adjacent carbon is allylic