Content:
Alkane:
Structure and physical properties
(boiling point and solubility),
Nomenclature (naming)
Preparation (hydrogenation of alkenes,
hydrolysis of Grignard reagents)
Alkane reactions (halogenation/free
radical substitution, combustion)
Sources and uses
Bpt vs C-chain length
As Chain length^, # e-^, therefore LDF's^, so bpt^
Source: http://www.chemistryrules.me.uk/junior/organic.htm
Very good for introductory organic Chem!
As branching ↑, Surface area ↓,
hence VdW’s ↓, bpt ↓
^^ Reference
http://chemed.chem.wisc.edu/chempaths/GenChem-Textbook/Properties-of-Alkanes-917.html
Nomenclature for alkanes
• Find the longest carbon sequence (either a chain or
within a ring). That forms the ROOT / PARENT /
PRIMARY name.
• Name ‘branches’ as prefixes in alphabetical order
(note: do not use di, tri, tetra etc in the alphabetical
ordering)
• Use numbering so numbers are as low as possible.
• Ring structure have the prefix ‘cyclo’ rest of name.
• Letters are separated from numbers using a hyphen
• Numbers are separated from each other using a
comma
• ‘special groups’ (commonly occur, so given their
own name and they remain in widespread use)
https://www2.chemistry.msu.edu/faculty/reusch/virttxtjml/nomen1.htm
Very good page for nomenclature
Hydrocarbon preparation
• Hydrogenation of alkenes.
H
H
+
C C
H
H H
metal catalyst:
Pt or Rh or Ni
H
H H
H
H
H H
• Hydrolysis of Grignard reagents.
Grignard reagent
(organo magnesium)
Bt
+
+
Mg in dry
ether
BrMg
-
+
H
O
H
H
( + MgOHBr)
Note: This example shows a trivial example You would NEVER do this
to get a simple, readily available alkene You would only do it to make a rare or complicated alkane.
New bond
+
•
Or by other Grignard reactions:
OTs
+
BrMg
Grignard
(organo magnesium)
Alkane reactions
(Functionalisation of alkanes)
http://driesnuyts.blogspot.com/2012/04/alkanes-and-radicals-introduction.html
Combustion of alkanes
• Fuels (e.g. the RM1.92 RM2.10 Ron95) are
made up mostly of alkanes.
In excess oxygen
• CnH2n+2 + (1.5n+½)O2  nCO2 + (n+1)H2O
• The process is exothermic and causes a large
increase in volume and entropy.
Application: Sources and uses
• Uses: as fuels (e.g. Kerosine), solvents (e.g.
hexane), chemical feedstock
• Source: Primarily from the Crude oil which is a
complicated mixture of many compounds.
Some long hydrocarbons are broken up to
produce smaller, often more useful
hydrocarbons.
Conformations
• Alkane chains and rings are in a constant state
of motion/vibrations (due to background
thermal energy). Alkane vhains can rotate
about the C-C and rings can flex. Each
‘snapshot’ of the orientation of the molecule
has it’s own energy.
Alkane ‘chain’ conformers
1 cal
= 4.18 Joules
http://chemistry.umeche.maine.edu/CHY251/Butane.html
Alkane ring conformers
Energy profile of cyclohexane conformers…
http://www.stolaf.edu/depts/chemistry/courses/toolkits/247/js/cyclohex/
Nomenclature practice:
Alkenes
H
H
H
H
H
H
Ethene
H
H
C C H
H H H
Butene?
H
C C H
H
H
H
Propene
H
C C
C H
H H
H
C C
C C
C C
H
H
But-1-ene
H
trans-But-2-ene
3-Methyl-cyclohexene
Bpt of alkenes v.similar to alkanes.
Why?
Similar # e- (2 less than alkane)
Dehydration of alcohols
Use a dehydrating agent e.g. c.H2SO4 or c.H3PO4
or Al2O3 and heat. Different temps used can give
different products!!!
http://www.transtutors.com/chemistry-homework-help/alcohols/dehydration-of-alcohols.aspx
Dehydration of alcohols
Mechanism (how reaction happens)
http://www.education.com/study-help/article/nomenclature-structure/
Prep of alkenes Dehydrohalogenation
http://www.personal.psu.edu/users/t/h/the1/e2.htm
Dehydration of alcohols
Zaitsev's (Saytzeff) rule: For Dehydration and
dehydrohalogenation, the more substituted alkene
product is major product
http://www.mhhe.com/physsci/chemistry/carey/student/olc/graphics/carey04oc/ref/ch05eliminationreactions.html
Markovnikov Rule:
Cation (usually H+) adds into the compound to
make the most substituted carbocation.
Familiarity with carbocation stability is crucial in organic chemistry
https://www2.chemistry.msu.edu/faculty/reusch/virttxtjml/addene1.htm
Addition reactions of alkenes (X-Y)
http://www.chemguide.co.uk/mechanisms/eladd/whatis.html#top
http://www.chemguide.co.uk/mechanisms/eladd/whatis.html#top
Overall:
Can also occur via free radical mechanism
http://mhschemf6.blogspot.com/2011/05/alkene.html
Markovnikov Rule:
Cation (usually H+) adds into the compound to
make the most substituted carbocation.
Addition reactions of alkenes (X-X)
http://www.masterorganicchemistry.com/reaction-guide/bromination-of-alkenes-with-br2-to-give-dibromides/
Aleken + AQ Br2
• Gives a halohydrin (+ monobormo product)
http://en.wikibooks.org/wiki/Organic_Chemistry/Introduction_to_reactions/Halohydrins
Alkenes with conc. H2SO4
• See the similarity with the other conc. acids
https://www2.chemistry.msu.edu/faculty/reusch/virttxtjml/addene1.htm
C=C with KMnO4 (Baeyer test)
COL/RT condition: Purple colour of
permanganate solution decolourises on addition
to colourless alkene. Brown solids (MnO2)
procuded in neutral or alkaline conditions. Very
pale pink (will look almost colourless, in acidic
solution)
C=C with KMnO4 (Baeyer test)
HOT CONCENTRATED and ACIDIFIED KMnO4
http://www.chemguide.co.uk/organicprops/alkenes/kmno4.html
Ozonolysis (cleavage using ozone, O3)
http://en.wikipedia.org/wiki/Ozonolysis
Ozonolysis (cleavage using ozone, O3)
Overall:
http://en.wikipedia.org/wiki/Ozonolysis
As with all info on these slides, you should try and condense it
into simple reaction equations (as above) to help begin the
process of ‘connecting’ reactions. The overall equation is just to
summarise the reaction and remind you.
Alkene (partial summary of) reactions.
C=C - Applications and use
• Polymers (addition polymers – poly(styrene),
PVC, poly(propene)
• Raw materisals for making R-X, R-OH and
carbonyls
2.3 Aromatic compounds
• Answers to practice (L to R, top to bottom)
Butane
2-Methylbutane
3,3-Diethyl-4-methylhexane
Propylcyclopentane
(3-Methyl-2-cyclopentylheptane
3,4-Diisopropyl-2,5,6-trimethylheptane
Aromatic compounds (Benzene)
http://en.wikibooks.org/wiki/A-level_Chemistry/OCR_%28Salters%29/Reactions_of_arenes
3.0 Aliphatic alcohols
Nucleophilic substitution in
alcohols
(1)
H
R
C : O

+
H
H
H
(2)
.. ( _ )
Nu
_
R
C
H
(1) New bond forms between C and Nu (sharing Nu's e- pair)
(2) Old bond breaks between C and O
Nu
+
:OH