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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
•C• •
•
×HH H C H
H
•×ו•
•××
Carbon AtomCarbon with Hydrogen
Hydrogen Atom
• C : C • • •
• • C : : C• •• •
Carbon with Carbon
C C C C C C
single double triple
ORGANIC STRUCTURES ( a ‘short hand’)
H H H H-C-C-C-H
H H H-C-H H
or
CH3 – CH2 – CH2
CH3
or
CH3CH2CH2CH3or
all H’s understood
T h e P r o b l e m w i t h P r e f i x e s
C 5 H 1 2 I s o m e r s ( p o s i t i o n a l )
C H 3 C H C H 2 C H 3
C H 3
C H 3 C H 2 C H 2 C H 2 C H 3 C C H 3C H 3
C H 3
C H 3
P e n t a n e I s o p e n t a n e N e o p e n t a n e
( M e t h y l b u t a n e ) ( D i m e t h y l p r o p a n e )
Positional Isomers of the Alkanes # of C’s Formula # of Isomers
1 2 3 4 5 6 7 8 9
101520
CH4 C2H6 C3H8 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 Parent name Derivation
1 meth- methe-(Gr.) 2 eth- aither(Gr.) 3 prop- protos + pion(Gr.) 4 but- butyrum(Lat.) 5 pent- pente(Gr.) 6 * hex- hex(Gr.) 7 hept- hepta(Gr.) 8 oct- okto(Gr.); octa(Lat.) 9 non- novem(Lat.) 10 dec- deka(Gr.); decem(Lat.) *NB. no ‘sex-’ (Lat.)
The First 10 Straight - Chain AlkanesName Molecular Formula
Methane Ethane Propane Butane Pentane Hexane Heptane Octane Nonane Decane
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 alkanes of hydrocarbons: alkenes alkynes aromatics
Origin of Hydrocarbons
H y d r o c a r b o n s ( A l k y l )
S t r u c t u r e B o n d “ S u f f i x ” E x a m p l e s
C C S i n g l e _ _ _ a n e B u t a n e , i s o o c t a n e
C C D o u b l e _ _ _ e n e P o l y s t y r e n e , p r o p y l e n e ,
- c a r o t e n e
C C T r i p l e _ _ _ y n e A c e t y l e n e ( e t h y n e )
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 ‘iso-’, ‘neo-’, ‘tert-’ chemical -OH & C=O vs. -COOH b. geometrical: ‘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• 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
Examples R
C C C C
R R R
R R
R
R
R
R
trans cis
ortho- meta- para-
= cyclo
cis- or trans- fatty acids
PABA = para-amino benzoic
acid (in sunscreen)
hexane butane pentane
cyclo
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 ‘Suffix’ ‘Prefix’ Examples R – X
R – OH
R – OR
R – NHR
halocarbon -halide halo- PVC,
alcohol -ol hydroxy menthol,
ether -ether alkoxy Methyl-t-butyl ether (MTBE); octane enhancer
amine am(ine) amino- adrenaline
perchloro- ethylene
ethanol cholesterol
nicotine
cocaine
Organic Functional Groups
Functnl Grp Generic ‘Suffix’ ‘Prefix’ Examples
R – C = O
R – C = O
H
R
aldehyde -al acyl citronellal
ketone -one ----- cortisone
retinal formaldehyde
acetone testosterone
Organic Functional Groups
Functnl Grp Generic ‘Suffix’ ‘Prefix’ Examples R – C = O
R – C = O
R – C = O
OH
OR
NR2
carboxylic -oic carboxyl acetic acid
ester -oate ------ phthalates
amide -amide amido- DEET
acid ASA
(acid + polyester
(acid+
fatty acids
alcohol) ethyl acetate
Common Names vs. IUPAC
• Acetone (common solvent) is propanone
• Acetic acid (in vinegar) is ethanoic acid
• Benzene (potent carcinogen) is 1,3,5-cyclohexatriene
• 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!