Chapter 24: Organic chemistry
Chemistry 1062: Principles of Chemistry II
Andy Aspaas, Instructor
Carbon
• Carbon: central element of organic chemistry
– Organic compounds: compounds containing
carbon-carbon bonds
• 4 valence electrons: 4 must be shared from other
atoms
– 4 single bonds (tetrahedral)
– 1 double bond, 2 single bonds (trigonal planar)
– 2 double bonds (linear)
– 1 triple bond, 1 single bond (linear)
Hydrocarbons
• Hydrocarbon: molecule that contains only carbon
and hydrogen atoms
– Saturated hydrocarbons: only C–C single bonds
• May be cyclic or acyclic
– Unsaturated hydrocarbons: contain some carboncarbon double and/or triple bonds
– Aromatic hydrocarbons: contain benzene rings
– (Non-aromatic hydrocarbons are aliphatic)
Alkanes and cycloalkanes
• Alkanes are acyclic saturated hydrocarbons
• Cycloalkanes are cyclic saturated hydrocarbons
• Molecular formula: indicates only type and quantity
of atoms in a molecule
• Structural formula: indicates connectivity in the
molecule (which atoms are bonded to which)
– Structural formulas look like Lewis structures
– Condensed structural formulas don’t draw the
bonds, but still indicate connectivity
Straight-chain alkanes
• Straight-chain alkanes (or normal alkanes) have all
carbons in a row
• n- at beginning indicates straight-chain (normal)
• General formula: CnH2n+2
Name
Methane
Molecular formula
CH4
Structural formula
CH4
Ethane
C2H6
CH3CH3
Propane
C3H8
CH3CH2CH3
n-Butane
C4H10
CH3(CH2)2CH3
Straight-chain alkanes (5 C through 10 C)
• For straight-chain alkanes 5 C through 10 C, use
Greek prefix followed by -ane
Name
Molecular formula
Structural formula
n-pentane
C5H12
CH3(CH2)3CH3
n-hexane
C6H14
CH3(CH2)4CH3
n-heptane
C7H16
CH3(CH2)5CH3
n-octane
C8H18
CH3(CH2)6CH3
n-nonane
C9H20
CH3(CH2)7CH3
n-decane
C10H22
CH3(CH2)8CH3
Isomerism in alkanes
• n-Butane has a contsitutional isomer (same number
and kind atoms, different bonds)
– Same molecular formula, different structural
formula
• Isobutane: branched, all carbons not in a row
CH3(CH3)CHCH3 (parentheses mean group is not
in the main chain)
CH3
H3C C CH3
H
Branched alkanes
• More complex branched alkanes require different
naming rules
– Any of the straight-chain alkanes can be made
into “substitutents” - or branches off a main chain
– Methane becomes methyl as a branch (—CH3)
– Ethane becomes ethyl as a branch (—CH2CH3),
etc
Naming complex branched alkanes
• Start by identifying the longest carbon chain
• Identify branches off the longest chain as their
substituent name (methyl, ethyl, propyl, etc)
• Number longest chain starting at end closest to the
first branch
• Name the compound, starting with branches and
indicating the number on the main chain to which
the branch is attached
Cycloalkanes
•
•
•
•
•
Saturated hydrocarbons which form a ring of carbon atoms
General formula CnH2n
Prefix name with cyclo- and name as if straight chain
E.g. cyclobutane (4 carbons); cyclohexane (6 carbons)
Any organic molecule can be drawn as a line-angle formula,
where carbons and hydrogens are not explicitly shown.
– Line-angle drawing of cyclohexane is simply a hexagon
– Practice drawing!
Alkenes and alkynes
• Alkenes and alkynes: unsaturated hydrocarbons
• Typically more reactive than alkanes (reactions can
occur at carbon-carbon double and triple bonds)
– Hydrogenation: addition of two hydrogen atoms
across a double bond
• Alkenes: general formula CnH2n just like
cycloalkanes
– Names end with -ene (compared to -ane ending
of alkanes)
Naming alkenes and alkynes
• Ethene is the simplest alkene (CH2=CH2)
– Common name is “ethylene”
• When there are more than one possible place to put
the double bond, it’s location must be indicated
– Start numbering carbons at end closest to the
double bond, and indicate the lower-numbered
carbon involved in double bond
– Ex. 1-butene: CH2=CH–CH2–CH3
2-butene: CH3–CH=CH–CH3
• Alkynes are named the same way, with -yne instead
of -ene
Aromatic hydrocarbons
• Benzene ring: six-membered carbon ring with
alternating single- and double-bonds
H
C
H
H
H
C
C
C
C
C
H
H
Nomenclature of aromatic hydrocarbons
• For singly substitued benzenes, use substituent
names and benzene as the suffix (ex.
Methylbenzene, ethylbenzene, etc.)
• When 2 identical groups are substituted on a
benzene, ortho-, meta-, and para- are used to
differentiate the isomers
• Multiple substituents require the benzene ring to be
numbered from 1-6 so that the substitutents get the
smallest possible numbers
Hydrocarbon derivatives
• Most organic molecules contain elements other than
carbon and hydrogen
• Heteroatom: atom that’s not C or H in an organic
molecule
• Functional group: common grouping of atoms which
reacts in a particular way
• Oxygen-containing functional groups are the most
common
Oxygen-containing functional groups
• Molecule fragments which symbolize oxygencontaining functional groups
• R and R’: symbols for general hydrocarbon groups
Aldehyde
O
R C H
Ether
R O R'
Ester
O
R C O R'
Ketone
O
R C R'
Carboxylic
acid
O
R C OH
Alcohol
R OH
Alcohols
• Alcohol: R–OH functional group
• Named with similar rules to hydrocarbons
– Main chain must contain carbon bonded to –OH
– Suffix -ol on chain name
– Position of –OH group indicated by number (omit
if unnecessary)
• Ex. Methanol, ethanol, 2-propanol
Ethers
• Ether: R–O–R’
• Common name: list the two R groups and suffix with
“ether”
– Ex. Methyl ethyl ether, diethyl ether
• IUPAC name: alkoxy derivative of longer chain
– Ex. Methoxy ethane, ethoxy ethane
• Diethyl ether (or just ‘ether’) used as solvent,
previously an anesthetic
Aldehydes
• Aldehydes, ketones, carboxylic acids, and esters all
contain a carbonyl group (C=O double bond)
• Aldehyde: carbonyl with a hydrogen
O
attached
R C H
– Usually abbreviated –CHO
– Methanal: CH2O (common name: formaldehyde)
– Ethanal: CH3CHO
(common name: acetaldehyde)
Ketones
• Ketone: carbonyl with two hydrocarbon groups
attached
O
R C R'
– Abbreviated –CO–
– Named with -one suffix on stem name, number
indication position of carbonyl
• Propanone: CH3COCH3 (common name: acetone)
• 2-butanone: CH3COCH2CH3
(common name: methyl ethyl ketone)
Carboxylic acids
• Carboxylic acids contain a carboxyl group, –COOH
O
• Named like aldehydes, but with
‘-oic acid’ as suffix
R C OH
• Many have common names
• CH3COOH: ethanoic acid - vinegar
(common name: acetic acid)
• CH3(CH2)2COOH: butanoic acid - rancid dairy
(common name: butyric acid)
Esters
• Ester: RCOOR’
• Formed by reaction of alcohol with carboxylic acid
– Ex. Ethanol + Acetic acid  Ethyl acetate
CH3CH2 OH
O
HO C CH3
CH3CH2
• Pleasant, fragrant smells
• Many familiar fruit smells are esters
O
O C CH3
H2O
Nitrogen-containing functional groups
• Amine: RnNH3-n
R NH2
H
R N R'
R''
R N R'
primary
(1°)
secondary
(2°)
tertiary
(3°)
• Generally sharp- or strong-smelling
• Ammonia: NH3
• Triethylamine (CH3CH2)3N smells like dead fish
Amides
• Amides: RCONH2 or RCONHR’
O
R C NH2
O
H
R C N R'
• Formed by reaction of amine with carboxylic acid,
similar to ester formation