ORGANIC CHEMISTRY

CHAPTER 25
I. Introduction

A. WHAT IS ORGANIC CHEMISTRY?

1. The word organic is used in the “real world” rather loosely.

Organic food?
Organic gardening?

2. At one time organic chemistry was the study of compounds derived from living things. Many organic compounds are derived from living things, but not all.

3. Organic chemistry is the study of the compounds of carbon.

4. More than 95% of all known compounds contain C.

5. On Earth all life forms are based on C


B. UNIQUENESS OF CARBON

1. VAST NUMBER OF ORGANIC COMPOUNDS:
>6,000,000 PREPARED IN LAB
>15,000,000 KNOWN


2. VAST VARIETY OF ORGANIC COMPOUNDS


3. CARBON FORMS STABLE COMPOUNDS WITH
MANY ELEMENTS:

a. MOST COMMON: H, O, N, S, P

b. OTHERS: Na, Mg, Ca, Co, etc.

4. CARBON FORMS STABLE “CHAINS” WITH
OTHER CARBON ATOMS

5. ALTHOUGH CARBON ALWAYS FORMS FOUR
CHEMICAL BONDS IN NEUTRAL ORGANIC
COMPOUNDS, IT MAY FORM SINGLE, DOUBLE, OR TRIPLE BONDS TO A SINGLE
ATOM:



a. 4 SINGLE BONDS TO 4 DIFFERENT ATOMS:









b. 1 DOUBLE BOND AND 2 SINGLE BONDS TO 3 DIFFERENT ATOMS:



c. 1 TRIPLE BOND AND 1 SINGLE BOND TO 2
DIFFERENT ATOMS:



d. 2 DOUBLE BONDS TO 2 DIFFERENT ATOMS:



II. Hydrocarbons-compounds composed of carbon and hydrogen atoms.

A. The Alkanes-names always end in ANE

1. Saturated=contains only single bonds to C, have as many H atoms per molecule as is possible.

2. Representations:

Molecular formula=CH₄, C₂H₆, C₃H<sub>8



Structural formula=show bonds as lines, show atoms using their symbol. Remember: C must have 4 bonds!</sub>



Condensed=no bonds shown, but atoms in the correct order.



3-D like



3. Naming-Based on the longest chain of C atoms in the compound. Page 965-Table 25.1

MethANE EthANE PropANE


When we get to C₄H₁₀ there is more than one way to put the compound together.

Isomers=compounds that have the same molecular formula, but different structures.

One of the reasons for the vast number of organic compounds is the existance of isomers.

From the formula C₁₀H₂₂ there are 75 different possible compounds!



Pentane



Isopentane

4. Some groups have frequently used common names. Page 969-Table 25.2



5. Properties of Alkanes

Boiling points generally increase with increasing #C atoms.

C 1--> 4----> gases at RT
C5-->C16----> liquids at RT
>C16----> solids at RT

Less dense than water (< 1.0 g/mL)

Insoluble in water. They are nonpolar and water is very polar. They dissolve in nonpolar solvents such as CCl₄.

Physiological Properties

Some of the gases are anesthetics.
Can cause asphyxiation by excluding O₂.
Liquids dissolve body oils on the skin.
Heavier liquids and semisolids act as skin emollients, ie. mineral oil, petroleum jelly.

React readily with oxygen to form CO₂, H₂O and energy.

CH₄ + 2 O₂ -----> CO₂ + 2 H₂O + ENERGY
(natural gas)

III. Cyclic Hydrocarbons-hydrocarbon chains with the ends connected. Called cycloalkanes if only single bonds.


These compounds are usually represented by a geometric shape, the number of sides corresponding to the number of C atoms in the compound. See page 969.

In nature the 5 and 6 C compounds are the most common.

Name= cyclo + alkane with that # of C atoms.

Cyclopropane=smallest possible and very unstable

=

IV. Alkenes and Alkynes

Unsaturated hydrocarbons, those that contain either C to C double or triple bonds.

More H atoms can be added to these compounds.

1. Alkenes-contain at least one C=C


EthENE PropENE
(ethylene) (propylene)


2. Alkynes-hydrocarbons which contain ato least one .


EthYNE PropYNE
(acetylene)

3. Unsaturated compound can add hydrogen and become saturated. Called hydrogenation.




4. Properties of Alkenes and Akynes

Same trends as for alkanes

V. Aromatic Hydrocarbons-Derived from the compound called benzene.

1. Has a molecular formula of C₆H₆. Doesn’t fit the properties of other hydrocarbons.

Unsaturated but don’t add H₂ readily

2. Structure for benzene proposed by August Kekule in 1865.


Modern structure



Not alternating double and single bonds
Called aromatic bonding

3. Why aromatic?

Many of the first aromatic compounds discovered had pleasant odors--->aromatic

Now--->Aromatic means compounds derived from benzene

VI. Chlorinated Hydrocarbons-contain the element Cl in addition to C and H.

1. Usually prepared by reaction of Cl₂ with hydrocarbons.

2. Many chlorinated hydrocarbons are used by man.

CH₂Cl₂=methylene chloride, used in paint thinner

CHCl₃=chloroform, used as an anesthetic

3. Freons-contain both chlorine and fluorine

CF₂Cl₂=freon 12

Once used as refrigerants and propellants in spray cans.

Insoluble in water

Inert toward most substances

React with ozone (O₃)