INTRODUCTION TO

ORGANIC CHEMISTRY

• Organic chemistry - is chemistry of most of the compounds, containing carbon. • Compounds with at least one carbon - carbon bond - are for sure organic.• The term “Organic” was applied to substances, isolated from living things by Jons Berzelius (Beginning of the 19th century).• These compounds were though to be arisen from a “Vital force”,responsible for the process of life.• 1828 - Friederich Wohler converted inorganic ammonium cyanate to organic urea. • 1856-1863 – MarcellinBerthelot synthesized organic acetylene from inorganic compounds.• The theory of vital force was ruled out.

What is Organic chemistry?

Wöhler Synthesis of UreaThe consecutive reactions are:

KCN + PbO2 KOCN + PbOPotassium cyanide Lead(IV)oxide Potassium cyanate Lead(II)oxide

2KOCN + (NH4)2SO4 K2SO4 + NH4OCNPotassium cyanate Ammonium sulphate Potassium sulphate Ammonium cyanate

NH4OCN Ammonium cyanate Urea

Organic Compounds

• It used to be thought that only living things could synthesize the complicated carbon compounds found in cells

• German chemists in the 1800’s learned how to do this in the lab, showing that “organic” compounds can be created by non-organic means.

• Today, organic compounds are those that contain carbon. (with a few exceptions such as carbon dioxide and diamonds)

Organic Compounds- Organic compounds can be found in

Fats, carbohydrates and proteins.

Importance of Organic Compounds

Why is it important?

>90% of compounds are organic

Organic compound : • is a compound made from carbon atoms.• has one or more C atoms. • has many H atoms.• may also contain O, S, N, and halogens.

Common Elements in Organic Compounds

- The 6 most common elements that make up organic compounds are:

Carbon

SulfurNitrogen Phosphorous

Hydrogen Oxygen

Typical Organic Compounds

Typical organic compounds

• have covalent bonds.

• have low melting points.

• have low boiling points.

• are flammable.

• are soluble in nonpolar solvents.

• are not soluble in water. oil (organic) and water (inorganic)

Organic vs. Inorganic

• Propane, C3H8, is an organic compound used as a fuel.

• NaCl, salt, is an inorganic compound composed of Na+ and Cl- ions.

Comparing Organic and Inorganic Compounds

Copyright © 2005 by Pearson Education, Inc.Publishing as Benjamin Cummings

Learning Check

Identify each characteristic as most typical of compounds

that are 1) inorganic 2) organic.

A. has a high melting point

B. is not soluble in water

C. has a formula CH3─CH2─CH3

D. has a formula MgCl2

E. burns easily in air

F. has covalent bonds

1

1

2

2

2

2 (some 1)

Formulas of Organic Compounds

In organic chemistry formulas of compounds can be represented in different ways:

• Emprical or the simplest formula

• Molecular formula

• Structural formula

Emprical Formula

• An emprical formula gives us the kinds of atoms and the simpest whole number integer ratio between them.

• For example it is ½ in ethylene,C2H4.

• It is 1 in acetylene, C2H2.

• The emprical formula of two different compounds may be the same as in the case benzene,C6H6 and acetylene, C2H2.Because the simplest whole number integer ratio is 1 for these compounds.

Molecular Formula

• A molecular formula simply counts the numbers of each sort of atom present in the molecule, but tells you nothing about the way they are joined together. • Molecular formulas are very rarely used in organic chemistry, because they don't give any useful information about the bonding in the molecule.About the only place where you might come across them is in equations for the combustion of simple hydrocarbons, for example:

Structural Formula

• A structural formula shows all the bonds in the molecule as individual lines.

• You need to remember that each line represents a pair of shared electrons.

• For example the formulas of ethylene can be represented:

C2H4 CH2

Molecular Emprical Structural

Formula Formula Formula

Examples of Empirical and Molecular Formula

If carbon and hydrogen are present in a compound in a ratio of 1:2, the empirical formula

for the compound is CH2. The empirical formula mass of this compound is:

12.0 + (2 x 1.0) = 14.0 g/mol If we know the molecular mass of the compound

is 28.0 g/mol then we can find the molecular formula for the compound.

MM = n x empirical formula mass 28.0 = n x 14.0

n = 2 So the molecular formula for the compound is 2 x

empirical formula, ie, 2 x (CH2) which is C2H4

Examples of Empirical and Molecular Formula

• There are many compounds that can have the empirical formula CH2. These include:

• C2H4 (ethene or ethylene) molecular mass=28.0g/mol and n=2

• C3H6 (propene or propylene) molecular mass=42.0g/mol and n=3

• C3H6 (cyclopropane) molecular mass=42.0g/mol and n=3

• C4H8 (butene or butylene) molecular mass=56.0g/mol and n=4

• and so on......

Calculating Empirical Formula from Percentage Composition

• Assume 100g of sample • Convert all percentages to a mass in grams, eg, 21% =

21g, 9% = 9g • Find the atomic mass of each element • Calculate the moles of each element present: • n = mass ÷.at.wt • Divide the moles of each element by the smallest of

these to get a mole ratio • If the numbers in the mole ratio are all whole numbers

(integers) convert this to an empirical formula • If the numbers in the mole ratio are NOT whole

numbers, you will need to further manipulate these until the mole ratio is a ratio of whole numbers (integers)

Example 1A compound is found to contain 47.25% copper and 52.75% chlorine. Find the empirical formula for this compound.

Thus the emprical formula of this compound will be CuCl2.

Element Cu Cl

mass in grams 47.25 52.75

At.wt. 63.6 35.5

Mole=mass/at.wt 47.25 ÷ 63.6 = 0.74

52.75 ÷ 35.5 = 1.49

Divide by lowest number

0.74 ÷ 0.74 = 1

1.49 ÷ 0.74 = 2.01 = 2

Hydrocarbons• Hydrocarbons are simple organic compounds which

contain only carbon and hydrogen.  • If the carbon atoms are linked in chains, the

compounds are called aliphatic compounds; if the atoms are linked in rings, the compounds are called alicyclic.

• The chain compounds, or aliphatic compounds, may be further classified on the basis of the individual carbon-to-carbon bonds. 

• Every carbon atom can form four bonds to other atoms thus the noble gas configuration is reached (8 outer electrons). 

• Every hydrogen atom forms one bond producing 2 outer electrons, the most stable state for hydrogen.

SATURATED HYDROCARBONS (ALKANES)

• Chain compounds in which all carbon-to-carbon bonds are only simple single bonds are called ALKANES. 

• These compounds are also called saturated hydrocarbons, because each carbon-to-carbon bond is a single bond, and the valence of the carbon atom is, therefore, saturated.  

• No more atoms can be bonded to the atoms in the compound, without breaking the compound into two or more fragments. 

ALKANES

• Almost all other organic compounds can be named as derivatives of these simple hydrocarbons.  

• Alkanes which have long carbon chains are often called paraffins in chemical industry. 

• The most simple alkane is methane with the formula CH4.

• The second alkane is ethane with the formula C2H6.  

• The general formula of alkanes is CnH2n+2.• Alkanes occur in what is called a homologous series.• Each successive compound differs from the one before

it only by a CH2

Line Bond Representation and Condensed Formula

The First Four Alkanes

The Straight(continuous) Chain Alkanes

Homologous series• The ability of carbon atoms to form chains leads to the

existence of a series of compounds that have the • same functional group (and hence similar chemical

properties) and • only differ from each other by the presence of an

additional carbon atom and its two associated hydrogen atoms in the molecule (which causes the physical properties to change in a regular manner).

• A series of compounds related in this way is said to form an homologous series.

• The alkanes are the simplest example of such a series, but others include the alkenes, the alcohols and the carboxylic acids.

• These series can be thought of as different 'families' of organic compounds

Homologous series

In these homologous series:• successive compounds differ from each other

by a -CH2- unit (known as a methylene group)

• the compounds can all be represented by a general formula (in the case of the alkanes CnH2n+2; if n = 3, then the formula is C3H8)

• the compounds have similar chemical properties• successive compounds have physical

properties that vary in a regular manner as the number of carbon atoms present increases.

Homologous series

• The point about chemical properties is best illustrated by the sections that follow, on different homologous series.

• The changes in physical properties are a result of the changes that occur in the strength of van der Waals' forces with increasing molar mass and in some cases a change in molecular polarity.

• The simplest illustration of the effect of chain length on physical properties is the variation of the boiling point of the alkanes with the number of carbon atoms in the chain, as illustrated in Figure 1002.

The Saturated Hydrocarbons, or Alkanes

Name Molecular Formula

Melting Point (oC)

Boiling Point (oC)

State at 25oC

methane CH4 -182.5 -164 gas ethane C2H6 -183.3 -88.6 gas propane C3H8 -189.7 -42.1 gas butane C4H10 -138.4 -0.5 gas pentane C5H12 -129.7 36.1 liquid hexane C6H14 -95 68.9 liquid heptane C7H16 -90.6 98.4 liquid octane C8H18 -56.8 124.7 liquid nonane C9H20 -51 150.8 liquid decane C10H22 -29.7 174.1 liquid undecane C11H24 -24.6 195.9 liquid dodecane C12H26 -9.6 216.3 liquid eicosane C20H42 36.8 343 solid triacontane C30H62 65.8 449.7 solid

Cycloalkanes

• are cyclic alkanes.• have two hydrogen atoms fewer than the open

chain. (remember each carbon has 4 bonds)• are named by using the prefix cyclo- before

the name of the alkane chain with the same number of carbon atoms.

• General formula CCnnHH2n2n

– Five- and six-membered rings are the most common.

Drawing and Naming CycloalkanesDrawing and Naming Cycloalkanes

Cycloalkanes are represented by polygons. A Cycloalkanes are represented by polygons. A triangle represents cyclopropane, a square triangle represents cyclopropane, a square represents cyclobutane, a pentagon represents cyclobutane, a pentagon represents cyclopentane, and so on.represents cyclopentane, and so on.

Cyclic AlkanesCyclic Alkanes

Cyclopropane, C3H6

Cyclobutane, C4H8

Cyclopentane, C5H10

Cyclohexane, C6H12

Cycloheptane, C7H14

Remember, explicit (apaçık,aşikar) hydrogens are left out.

Line structureLine structureLine structureLine structure: A shorthand way of : A shorthand way of drawing structures in which atoms aren’t drawing structures in which atoms aren’t shown; instead a carbon atom is shown; instead a carbon atom is understood to be at each corner and understood to be at each corner and hydrogens are “understood”.hydrogens are “understood”.

Cycloalkanes

The structural formulas of cycloalkanes are usually

represented by geometric figures,

Cyclopropane CH2

CH2 CH2

CyclobutaneCH2 CH2

CH2 CH2

44

More Cycloalkanes

Cyclopentane CH2

CH2 CH2

CH2 CH2

Cyclohexane

CH2

CH2 CH2

CH2 CH2

CH2

References

• http://www.chemguide.co.uk/basicorg/conventions/draw.html

• http://www.3rd1000.com/chem301/chem301j.htm