Chapter 3Introduction 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) / Alkyl Substituent (R-) / Other Substituent (R-)
(“parent” carbon chains)
CH4 methane
CH3CH3 ethane
CH3CH2CH3 propane
CH3(CH2)2CH3) butane
C5 pentaneC8 octane
C6 hexaneC9 nonane
C7 heptaneC10 decane
/ (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


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 formula2D formula3D 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 formula2D formula3D formula

E.g. Propane: C3H8

Condensed formula2D formula3D 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 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?

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)attached to three carbons

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3.5 – 3.6 Classification of Alkyl Halides, Alcohols and Amine

Alkyl Halides / Alcohol / Amine
The functional group is a halogen (X = F, Cl, Br, I)


/ The functional group is hydroxyl (-OH)
R-OH


/ The functional group is a nitrogen atom.
RNH2, R2NH or R3N



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Nomenclature

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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

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

*Hydrogen bonding – strongest known dipole, due to having H on N or O

water ethyl alcoholdimethyl ether propane

H2OCH3CH2OHCH3OCH3CH3CH2CH3

B.P(oC)10078 -24-42

*van der waals interaction

Greater surface area, greater van der waals

Higher MW, higher B.P (if all polarity is equal)

Straight chain vs. branches

E.g. 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, +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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