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Chapter 3
Introduction to Organic Compounds
 Two types
◦ Saturated hydrocarbons
◦ Unsaturated hydrocarbons
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3.1 Alkanes
 Also referred as aliphatic hydrocarbons
 General formula: CnH2n+2 (straight chain) and CnH2n (cyclic)
Alkanes (RH)
(“parent” carbon chains)
CH4
methane
CH3CH3
ethane
CH3CH2CH3
propane
Alkyl Substituent (R-)
Other Substituent (R-)
(groups attached to parent)
CH3
meth (Me)
CH2CH3
ethyl (Et)
CH2CH2CH3 propyl (Pr)
(groups attached to parent)
F fluoro
Cl chloro
Br bromo
I iodo
CH3(CH2)2CH3) butane
C5 pentane C8 octane
C6 hexane C9 nonane
C7 heptane C10 decane
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Structure Presentation
E.g.
methane: CH4
All single carbon has four bonding position, completely saturated by the four hydrogen
atoms. There is only one possible arrangement of the atoms.
Condensed formula
2D formula
3D formula
CH4
E.g.
Ethane: C2H6
Only two carbon atoms are connected to each other and there are six possible
bonding sites. These are filled by the six hydrogen atoms
Condensed formula
2D formula
3D formula
2D formula
3D formula
E.g. Propane: C3H8
Condensed formula
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Because single bonds allow rotation, there are number of ways that alkanes can be
drawn using slightly different representation.
Constitutional isomers: Compounds that have the same molecular formula but different
structural formulas (a different connectivity of their atoms).
• For the molecular formulas CH4, C2H6, and C3H8, only one structural formula is
possible. There are no constitutional isomers for these molecular formulas.
E.g. How many alkane structures can you draw from C4H10? (*Hint: always start with a
straight chain carbon-carbon backbone)
E.g. How many isomers can you draw from C3H7Cl?
* Do cycloalkanes have isomers? YES
E.g. There are two possible ways to make ring using four carbon atoms of C4H8.
E.g
How many constitutional isomer can you draw from C5H10?
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3.2 – 3.4 IUPAC Rules for naming alkanes
1. Find the longest carbon chain (if there is a tie, choose chain with the most
substituent). Name parent
2. Number the carbon chain, starting from the end closest to the first substituent
3. Name and number the subtituents (use di, tri, tetra etc.., prefixes for groups that
appear more than once).
4. Alphabetize and list substituents before the parent name. Ignore all prefixes other
than iso.
E.g.
E.g
Draw a bond-line formula for 2-sec-butyl-3-bromohexane
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Type of carbons:
Primary (1o)
attached to one carbon
Secondary (2o)
attached to two carbons
Tertiary (3o)
carbons
attached to three
3.5 – 3.6 Classification of Alkyl Halides, Alcohols and Amine
Alkyl Halides
The functional group is a
halogen (X = F, Cl, Br, I)
Alcohol
Amine
The functional group is The functional group is a
nitrogen atom.
hydroxyl (-OH)
RNH2, R2NH or R3N
R-OH
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Nomenclature
3.7 The physical properties of alkanes, alkyl halides, alcohols, ethers and amines
Melting points/Boiling points
If CH4 molecules are strongly attracted to each other, then large amount of energy is
needed to separate them apart  higher boiling point
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Type of nonbonding interactions
A.
Ion-ion interaction (Na+ Cl-)
B.
Dipole-Dipole (polar interaction)
C.
Hydrogen bonding (OH, NH)
D.
Van der waals (vdw) (nonpolar molecules)
*Dipole – dipole interaction between polar molecules
Dipole-dipole interactions represent
moderate forces of attraction between
partially polarized bonds
*Hydrogen bonding – strongest known dipole, due to having H on N or O
B.P(oC)
water
ethyl alcohol
dimethyl ether
H2O
CH3CH2OH
CH3OCH3
CH3CH2CH3
100
78
-24
-42
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propane
*van der waals interaction
These are temporary fluctuations
of negative electron clouds from
one side to another, relative to
the less positive nuclear charge.
Greater surface area, greater van der waals
Higher MW, higher B.P (if all polarity is equal)
Straight chain
E.g.
vs.
branches
Rank the following molecules from high to low boiling point
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E.g. Match the given boiling point with the structures below and give a short reason for
your answer. (-7oC, 28oC, +80oC, +141oC, +142OoC)
Water solubility
“like dissolves like” and H2O is polar and can form H-bonds
Polar solute dissolves in polar solvent
Nonpolar solute dissolves in non polar solvent
E.g.
E.g. Predict the solubility of the following compounds in water. Describes any kind of
intermolecular forces that occurs
NaCl
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