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Chapter 3
Introduction to Organic Compounds
Two types
◦
Saturated hydrocarbons
◦
Unsaturated hydrocarbons
3.1 Alkanes
 Also referred as aliphatic hydrocarbons
 General formula: CnH2n+2 (straight chain) and CnH2n (cyclic)
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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
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
CH4
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3D formula
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
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 C4H11Cl?
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* 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 cyclic constitutional isomer can you draw from C5H10?
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.
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Type of carbons:
Primary (1o) attached to one carbon
Secondary (2o)
attached to two carbons
Tertiary (3o) attached to three carbons
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
hydroxyl (-OH)
group
is The functional group is a nitrogen
atom.
RNH2, R2NH or R3N
R-OH
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Nomenclature
3.8 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.
Hydrogen bonding (OH, NH, HF)
C. Dipole-Dipole (polar interaction)
D. Van der waals (vdw) (nonpolar molecules)
*Hydrogen bonding – strongest known dipole, due to having H on N or O or F
*Dipole – dipole interaction between polar molecules
Dipole-dipole interactions represent moderate
forces of attraction between partially polarized
bonds
*van der waals interaction
These are temporary fluctuations
of negative electron clouds from
one side to another, relative to
the less positive nuclear charge.
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Greater surface area, greater van der waals
Higher MW, higher B.P (if all polarity is equal)
Straight chain
water
B.P(oC)
E.g.
vs.
branches
ethyl alcohol
dimethyl ether
propane
H2O
CH3CH2OH
CH3OCH3
CH3CH2CH3
100
78
-24
-42
Rank the following molecules from high to low boiling point
E.g. Match the given boiling point with the structures below and give a short reason for your answer.
(-7oC, 28oC, +80oC, +141oC, +1420oC)
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