Problem Set Assignments/2009
• May 12 class: Chapt 1 #1,2; Chapt
2#6,8,18; Chapt 3 #3; Chapt 5 #26,30;
Chapt 9# 1,14; Chapt 12#1,18
• May 14 class: Chapt 6 #1,8; Chapt 8#1,21
• Answers posted on the course website
What will be on quizzes and exam?
•
•
•
•
•
Lecture material and PP slides
Problem set material
Explanations etc. from Demo’s
Material covered in “What’s in the News”
Questions: T/F; short answer and multiple
choice format
6. Organic Chemistry :
an overview
“carbon to candles”
chapter 6
All life depends on water and compounds of carbon
Organic chemicals are those compounds
containing carbon(at least 1 atom).
Originally organic compounds were thought to be
only from ‘living matter’, ie. containing a ‘vital force’.
( consider the symbolism of ‘organic foods’)
Probably ~10 million organic compounds known!
Inorganic compounds are compounds/molecules
that do not contain carbon.
HYDROCARBON COVALENT BONDING
H
•
•×•
×
×H
H • C ×H
•C•
ו
•
Hydrogen Atom
H
Carbon Atom
Carbon with Hydrogen
• •
•C:C•
• •
C
C
single
•
•
C::C
•
•
Carbon with Carbon
C
C
double
C
C
triple
ORGANIC STRUCTURES ( a ‘short hand’)
HHH
H-C-C-C-H
H H H-C-H
H
CH3 – CH2 – CH2
or
CH3
or
CH3CH2CH2CH3
or
all H’s understood
The Problem with Prefixes
C5H12 Isomers(positional)
CH3
CH3 CH2 CH2 CH2 CH3
CH3 CH CH2 CH3
CH3
Pentane
Isopentane
(Methyl butane)
CH3 C CH3
CH3
Neopentane
(Dimethyl
propane)
Positional Isomers of the Alkanes
# of C’s
Formula
# of Isomers
1
2
3
4
5
6
7
8
9
10
15
20
CH4
C 2H 6
C 3H 8
C4H10
C5H12
C6H14
C7H16
C8H18
C9H20
C10H22
C15H32
C20H42
1
1
1
2
3
5
9
18
35
75
4347
366,319
The International Union of Pure and Applied
Chemistry, beginning in 1892, has attempted to
systematize the naming of organic compounds.
This IUPAC system for organic nomenclature is still
in general use.
Here are a few basic rules:
1. Find the longest continuous chain of carbon atoms
and apply the appropriate ‘term’; this will be the
‘parent name’.
# of C’s
1
2
3
4
5
6
7
8
9
10
Parent name
methethpropbutpent* hexheptoctnondec-
Derivation
methe-(Gr.)
aither(Gr.)
protos + pion(Gr.)
butyrum(Lat.)
pente(Gr.)
hex(Gr.)
hepta(Gr.)
okto(Gr.); octa(Lat.)
novem(Lat.)
deka(Gr.); decem(Lat.)
*NB. no ‘sex-’ (Lat.)
The First 10 Straight - Chain Alkanes
Name
Methane
Ethane
Propane
Butane
Pentane
Hexane
Heptane
Octane
Nonane
Decane
Molecular Formula
CH4
CH3–CH3
CH3-CH2-CH3
CH3-CH2-CH2-CH3
CH3-CH2-CH2-CH2-CH3
CH3-CH2-CH2-CH2-CH2-CH3
CH3-CH2-CH2-CH2-CH2-CH2-CH3
CH3-CH2-CH2-CH2-CH2-CH2-CH2-CH3
CH3-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH3 CH3
CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH3
More than 10 C’s in the chain
• Undecane (11), dodecane (12)
tridecane(13),tetradecane(14),
pentadecane(15) hexadecane (16)
heptadecane (17), octadecane (18),
nonadecane(19)
• After C19, beyond the scope of CHEM
1003!
• C20H42 is eicosane
Where to start numbering?
• At the end of the chain with the most
branches
• 3-methylhexane
Families of compounds are compounds of similar
structure and therefore similar properties.
Hydrocarbons are composed exclusively of
carbon and hydrogen.
There are 4 sub-categories
of hydrocarbons:
alkanes
alkenes
alkynes
aromatics
Origin of Hydrocarbons
Hydrocarbons (Alkyl)
Structure
Bond
“Suffix”
C
C
Single
___ane
Butane,
isooctane
C
C
Double
___ene
Polystyrene,
propylene,
-carotene
C
C
Triple
___yne
Acetylene
(ethyne)
Examples
Additional Complications!
• Isomers!
Isomers are compounds that have the same
molecular formula but are ‘different’ in some
aspect of their structure, eg.
a. positional:
structural
chemical
b. geometrical:
‘iso-’, ‘neo-’, ‘tert-’
-OH & C=O vs. -COOH
‘cis-’, ‘trans-’
c. 3-dimensional(stereo-):
all chiral centers
mirror images (D/L; +/-)
only 1 center
epimers
Optical isomers
• Enantiomers: contain one chiral (Gr. “Chiros”
=hand) center and are non-superimposable mirror
images
• Are identical in all respects except for the
direction in which they rotate plane polarized light
• D and L isomers
• Arise from tetrahedral C with 4 different
substituents
Non-superimposable Mirror images
Amino Acids and Chirality
• All naturally occuring amino acids are the L
–isomers : rotate the plane of polarized light
in counterclockwise direction (Why??)
• Enzymes: many are chiral and are only
active for a specifically handed substrate
• Lock and key (hand in glove) mechanism
for activity
Drug activity and handedness
• L-Dopa is active vs. Parkinson’s disease
• Its mirror image D-Dopa is inactive
• “Chiral synthesis” of pharmaceuticals is a
multibillion $ operation
• Separations are costly and time consuming
Isomers with multiple (n) unique
chiral centres
• # of isomers possible =2n.
• These are diastereomers: have different mp,
bp
• Cholesterol has 8 chiral centres, hence 28=
256 possible isomers. But only one occurs
naturally!
Cholesterol : A steroid
• 8 chiral centres
• Geometrical isomers
• Simplest examples are cis-trans isomers
• Differ only in the spatial arrangement of atoms
Trans fats
geometrical isomers of cis fats (cis=same) , trans= opposite
Trans fats
• Produced by partial hydrogenation of polyunsaturated
vegetable oil
• Are solids-give longer shelf life to products
• Are worse than lard (sat’d fat) for your arteries!
• “Banned” in NYC as of Jan 1, 2008
Can we totally rid our diet of trans
fats?
• No, they occur naturally in small amounts
in beef tallow, butter, milk
• Arise from microbial hydrogenation of
polyunsaturated fats in the animals’
digestive system
• Ottawa City council has decided against a
“ban” (wisely)
Organic Nomenclature - Descriptors
R
C
R
Examples
C
C
R
trans
C
cis
R
cis- or transfatty acids
R
R
ortho-
R
R
R
R
meta-
para= cyclo
PABA = paraamino benzoic
acid (in
sunscreen)
hexane
cyclo butane
pentane
More Complex Organic Molecules
• Contain atoms other than C and H
• To understand their properties, they are
grouped according to the nature of these
atoms and how they are bonded
• Classified according to reactivity and
function, hence “functional groups”
A functional group is a small set of atoms, held
together by covalent bonds in a specific and
characteristic arrangement, that is responsible for
the principal chemical and physical properties of that
compound
Organic Functional Groups
Functnl Grp Generic
R–X
R – OH
R – OR
R – NHR
‘Suffix’ ‘Prefix’
halocarbon -halide
alcohol
-ol
Examples
halo-
PVC,
perchloroethylene
hydroxy
menthol,
ethanol
cholesterol
ether
-ether alkoxy Methyl-tbutyl ether (MTBE); octane enhancer
amine
nicotine
am(ine) amino- adrenaline
cocaine
Organic Functional Groups
Functnl Grp
Generic
R – C = O aldehyde
H
R–C=O
R
ketone
‘Suffix’ ‘Prefix’ Examples
-al
acyl
citronellal
retinal
formaldehyde
-one
-----
cortisone
acetone
testosterone
Organic Functional Groups
Functnl Grp
Generic
‘Suffix’ ‘Prefix’ Examples
R – C = O carboxylic -oic carboxyl acetic acid
acid
ASA
OH
fatty acids
R – C = O ester
OR (acid +
-oate
alcohol)
R – C = O amide
(acid+
NR2
-amide
------
phthalates
polyester
ethyl acetate
amido-
DEET
Common Names vs. IUPAC
• Acetone (common solvent) is propanone
• Acetic acid (in vinegar) is ethanoic acid
• Benzene (potent carcinogen) is 1,3,5cyclohexatriene
• Chloroform is trichloromethane
Candle Chemistry
• Candle waxes are mixtures of solid
saturated hydrocarbons (paraffins) and long
chain (C16 or more) monoesters.
• Combustion in air generates CO2, H2O, heat
and light
Wax Components (esters)
• Oleo Stearin or Oleo Stearate (palm
vegetable wax) mp 155-160oF
• Stearic acid is the common name for
octadecanoic acid (C18)
• Oleic acid is same as stearic acid, except for
a cis C=C at the C9 position of the chain
Dripless candles
• Made by “overdipping” a normal candle (wax mp.
135-145 F) with a higher melting (160-170 F)
• Candle burns down the middle leaving a hallow
rim/tube to hold the melted inner wax
• Or, try soaking a normal candle for 24 hours in
salt water (2 tbs. salt to 2 cups water) for 24 hours
• Demo!!
Salted candles don’t drip!
• Compare flame intensity
Why does salt make a candle burn
brighter?
• Wick absorbs the NaCl solution
• When the wax starts to burn, it excites the
sodium electrons to a higher energy level
• Visible light (yellow) is given off when
these electrons return to a lower E level
• Sodium D line at 589 nm (yellow) in visible
range of 700 (red) to 400 (violet);3p to 3s
Sodium D line
• Heat excites 2p electrons to 3p level
• Visible light (589 nm wavelength) is
emitted when these electrons come down to
the 3s level
• Recall electron configurations
• Na is 1s2, 2s2, 2p6, 3s1.
• Na+ has lost the 3s electron
Visible light
• Red is longest wavelength, violet is shortest
Why no drips?
• Flame is hotter and stronger with salt
present in the wick, hence melted wax on
top vaporizes and burns off before it drips
down the side!