01:160:307 Lecture 5: ch 5
1 May 2018
School
Department
Course
Professor
!
!
1!
Chapter 5 – Alkenes
Heinz D. Roth
E-mail [email protected]
Office Hours: Thu 2:30 – 5:30 pm; WR-384
Wright Rieman Building, Busch Campus
Summary
General
Industrial Production
Nomenclature
Physical Properties
Structure and Bonding
Bond Length Bond Strength
Acidity
Ethylene in Plant Physiology
Index of hydrogen deficiency
Reactions
General Facts & Terms
Alkenes contain one or more “double bonds”
(meaning that two carbons are connected by two bonds)
(details under Structure)
they are “unsaturated”
(meaning that they have fewer Hs than is possible, as in alkanes)
(details under Index of hydrogen deficiency)
they are “planar”
(meaning that the two carbons and all their substituents are in the same plane, no free
rotation: cis-trans isomerism
(details under Structure)
the alkene group is a “functional group”
(meaning that the double bond reacts readily)
(details under Reactions)
Industrial Production of Ethylene and its use
Ethylene is produced by “steam cracking” of petroleum or its fractions (Scheme on next page).
World production in 2016: 150x106 t; largest quantity of any organic chemical (see next page).
Ethylene is a Feedstock for Polyethylene
Most of the ethylene is used to produce “polyethylene”, an “addition polymer”; the monomers
simply add to the growing polymer chain; all atoms of the monomer are incorporated into the
polymer
ethylene monomer addition!dimer!
C C
H
H
H
H
2C C
H
H
H
H
C
H
H
C
H
H
!
!
2!
The overall polymerization process can be represented as:
The polymerization is induced by a catalyst (Ziegler-Natta, Nobel Prize 1963)
Polyethylene and derivatives, where one H is replaced by another group (X, e.g., Cl, OH, CH3,
many others) are the largest-volume commodity chemicals (>100x106 t).
Scheme of the industrial production of Ethylene
Nomenclature
Common nomenclature for alkenes replaces the corresponding alkane suffix –ane with –ylene:
ethane propane butane
ethylene propylene butylene
IUPAC nomenclature for alkenes replaces the alkane suffix –ane with –ene:
ethane propane butane
ethene propene butene
Rules for naming alkenes:
Rule 1: Find the longest chain that includes the entire double bond (both carbons).
Rule 2: Indicate the location of the double bond in the main chain by a number, giving the
double bond the lowest number possible.
Rule 3: Add substituents and their positions as prefixes to the alkene stem.
C C
H
H
H
H
nC
H
H
C
H
Hn
!
!
3!
n-hexane 3-methylhexane 3,4-dimethylhexane
!!!!!!!!!!!! !!!!!!!! !
1-hexene 4-methyl-1-hexene 2-ethyl-3-methyl-1-pentene
If the alkene is symmetric, count from the end that gives the first substituent the lower number.
!
The two carbons of the double bond in cycloalkenes are numbered 1 and 2.
1-hexene 2-hexene 3-hexene
NOTE: stereochemical designation still missing
Rule 4 ? BF p. 211:
“Number the carbons (1), locate and name substituents (2), locate the double bond (3), and name
the main chain.” ?
This is not a new rule but an incorrect, because backward, summary of rules 1 – 3:
[you need to 1) locate the double bond and
2) the substituents before you can
3) number the carbons !]
Rule 4: Designation of stereoisomers
cis/trans isomers are examples of diastereomers, or stereoisomers that are not mirror images of
each other. Remember?
In cycloalkenes, trans isomers are stable only for larger rings: it is unnecessary to specify cis- for
rings up to cycloheptene.
16
1
6
16
1
6
3-methyl-3-hexene
1
2
2
1
cyclopentene 3-methylcyclopentene
Document Summary
Office hours: thu 2:30 5:30 pm; wr-384. Bond strength (meaning that two carbons are connected by two bonds) (details under structure) Ethylene is produced by steam cracking of petroleum or its fractions (scheme on next page). World production in 2016: 150x106 t; largest quantity of any organic chemical (see next page). Most of the ethylene is used to produce polyethylene , an addition polymer ; the monomers simply add to the growing polymer chain; all atoms of the monomer are incorporated into the polymer. The overall polymerization process can be represented as: n. The polymerization is induced by a catalyst (ziegler-natta, nobel prize 1963) Polyethylene and derivatives, where one h is replaced by another group (x, e. g. , cl, oh, ch3, many others) are the largest-volume commodity chemicals (>100x106 t). Scheme of the industrial production of ethylene ethane ethylene ethane ethene propane propylene. Common nomenclature for alkenes replaces the corresponding alkane suffix ane with ylene:
