Problem Set Assignments/2009 May 12 class: Chapt 1 #1,2; Chapt 2#6,8,18; Chapt 3 #3; Chapt 5 #26,30;...

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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!