Transcript Functional groups

Organic Chemistry
The unique chemistry
of carbon
Learning objectives
Describe two reasons for abundance of carbon
compounds
Distinguish between inorganic and organic
carbon and other compounds
Distinguish between isomers and non-isomers
Describe differences between optical and
geometric isomerism
Distinguish between aromatic and nonaromatic
Identify common functional groups
One element – one branch of
chemistry
Organic compounds based on
carbon: 13 million and rising (fast)
 100,000 new
compounds synthesized
annually
All 91 other elements combined:
only 300,000 compounds
Factoids about carbon
Fairly abundant in earth’s crust – but
not enough to explain domination
Highly significant to life
Key element in the human organism –
and all others
“God’s goof”:
The absence of stable mass 5
C and O are abundant because the atom with
mass 5 is unstable
Otherwise atom building after the Big Bang
would have resulted in much heavier elements
The thoughts of a cosmological atheist Fred
Hoyle:
“Some supercalculating intellect must have designed the
properties of the carbon atom, otherwise the chance of my
finding such an atom through the blind forces of nature
would be utterly minuscule….The numbers one calculates
from the facts seem to me so overwhelming as to put this
conclusion almost beyond question”
Organic and inorganic carbon
Inorganic carbon: ionic compounds
where carbon is incorporated as
carbonate – CO32Organic carbon: compounds of
carbon with itself, hydrogen and
other elements – by far the most
important
Organic carbon forms a thin canopy
Unique (?) conditions on earth that
support life
Earth’s
surface organic
Earth’s
crust inorganic
Vitalism and organic chemistry
Inorganic compounds were salts of the earth

Stable and easily synthesized
Organic compounds were of living organisms

Fragile and not easily synthesized
Belief in Vitalism posited that only living
organisms possessed a vital force necessary to
create organic compounds
In 1828 urea was synthesized and vitalism was
on the way out
Seven ages of man - many ages of a
carbon atom
 Combustion: C + O2  CO2
 Neutralization by seawater: CO2 + Ca(OH)2  CaCO3 + H2O
 Reaction with acid rain: CaCO3 + H2SO4  CO2
 Photosynthesis: CO2  Organic compounds (OC)
 Vegetation decomposes: OC  fossil fuels (FF)
 Vegetation consumed by animal: OC  new compounds
(proteins, DNA etc.)
 Respiration: sugars  CO2 + energy
 Industrialization: FF  C, CO2 + energy
 Manufacturing: FF  Plastics, polymers, drugs etc.
 Waste disposal Fossil fuels, CO2
Two reasons why carbon is unique
Carbon can form four bonds – four
valence electrons
Carbon forms very strong bonds with
itself – chains, rings etc.
Classifying organic compounds
Hydrocarbons are the simplest
organic compounds
Contain only C and H
Simplest is CH4 (natural gas)
Intermediate C8H18 (petroleum)
Synthetic polymers contain
thousands of atoms
Alkanes
All bonds are single
Saturated
No new bonds can be added
General formula CnH2n+1
Summary of types
Representing molecules
Molecular formula

Shows atoms in the molecule
Structural formula

Shows how they are all connected
Condensed structural formula

Simplified representation of connections
Naming organic compounds
Meth - ane
Number of
carbon
atoms
Type of
compound
Numbers game: count the carbon
atoms in the chain
Saturation bonding:
Multiple bonds and unsaturation
Saturated: no more bonds can be added
Unsaturated: more bonds can be formed

More reactive compounds
Alkenes contain double bonds
Going bananas:
Ethylene and fruit ripening
Examples of alkynes
Isomerism
Same number and type of atoms
Different arrangements
Hydrocarbons can have straight and branched
chains
Isomers simplified
Alkane isomers
 General formula
CnH2n+1
Three isomers of pentane
 C5H12
Five isomers of hexane
 C6H14
Number of isomers mushrooms as
chain length increases
CH4 – 1 possibility
C2H6 – 1
C3H8 – 1
C4H10 – 2
C5H12 – 3
C8H18 – 18
C10H22 – 75
C20H42 – 366,319
Optical isomerism is a special
variation
Molecules exhibit handedness –
mirror images which are not superimposable
Must have tetrahedral carbon with
four different groups attached
This carbon is chiral
Isomers and reaction yield
Each chiral carbon produces two
isomers
If there are n chiral carbon atoms
there are 2n isomers
Optical isomers are important in
nature
Amino acids are building blocks of
proteins
Amino acids are chiral
Proteins contain hundreds –
thousands of amino acids
Getting the correct isomer is a big
deal
Geometric isomers:
Isomerism and a healthy diet
What’s with all this trans fats anyway?
Ask a Chicago Alderman
Different geometry - same attachments
Cis isomers:


Don’t pack together
Cis isomers have low viscosity - good
Trans isomers:


Pack together tightly
Trans isomers are solids - bad
Aromatic: the stuff of dreams
Benzene ring contains 6 C atoms
Bonding is resonant – more stable
than expected
All aromatic compounds contain at
least one benzene ring
Benzene, C6H6, is one of the most
important industrial chemicals
Toxicity of benzene
Benzene is regarded as a highly
carcinogenic substance
Use and disposal of benzene are
regulated
Compounds containing benzene
rings are not necessarily toxic
Functional groups
Chemistry of organic compounds is
determined by functional groups
Functional group is an atom or group
of atoms that are different from C
Heteroatoms confer very different
properties on the substance
Heteroatoms affect physical and
chemical properties
C2H6 (ethane) is a gas at RT
C2H6 is insoluble in water
C2H6O (ethanol) is a liquid at RT
C2H6O is soluble in water
 Differences
in cohesive forces: O-H bonds
are polar, C-H bonds are not
Functionalized hydrocarbons
Chlorocarbons and the environment
Important uses – important problems
 Solvents CH2Cl2
 Insecticides
DDT
 Refrigerants CFCs
Alcohols: hic
Functional group –OH
Polar molecules dissolve in H2O
Ethanol: good for your health/bad
for your health?
Smoke gets in my eyes: olefactory
pleasures of aldehydes
C=O is carbonyl group
Aldehyde contains RCHO
Formaldehyde is a preservative and a
product of burning wood
Acrolein is a product of barbequing
Common smells and flavours
Ketones
Ketone is R1R2CO
Acetone is a common solvent
Smell found in cinnamon
Raspberries
Carboxylic acids
Commonly found in citrus fruits and
any sour foods
Formic acid present in ant and bee
stings
Esters: sweet aromas and flavours
Ester group is R1COOR2
Sweet aroma in pineapples, jasmine
Synthetic versions are very common
Ethers
Ethers contain R1-O-R2
No -OH bonds
Not soluble in water
Anesthetics
Amines: the stench of death
Amines contain NR1R2R3
Rotting fish
Decaying flesh
Illicit drugs