Organic Compounds
Organic compounds are abundant in the world around us. Any compound containing carbon
atom(s) is classified as an organic compound. Some common organic compounds are proteins,
carbohydrates, fats, plastics, and fuels. Carbon is the third most abundant element in the human
body. The other elements that combine with carbon range from hydrogen to oxygen, nitrogen,
and sulfur in those compounds in the body. The range of elements that combine with carbon
outside the body include all the halogens, and phosphorus.
We'll begin with the compounds of carbon and hydrogen. Compounds containing only carbon
and hydrogen are called hydrocarbons. The simplest hydrocarbon contains one carbon atom and
four hydrogen atoms. The formula is CH4, and the name is methane. If we continue adding
carbon atoms and hydrogen atoms the formulas and names for the first ten hydrocarbons are;
Formula
CH4
C2H6
C3H8
C4H10
C5H12
C6H14
C7H16
C8H18
C9H20
C10H22
Name
Methane
Ethane
Propane
Butane
Pentane
Hexane
Heptane
Octane
Nonane
Decane
We can also write the formula as a condensed formula which shows us a little more information
for these compounds.
Formula
CH4
C2H6
C3H8
C4H10
C5H12
C6H14
Condensed Formula
CH4
CH3CH3
CH3CH2CH3
CH3CH2CH2CH3 or
CH3(CH2)2CH3
CH3CH2CH2CH2CH3 or
CH3(CH2)3CH3
CH3CH2CH2CH2CH2CH3 or
CH3(CH2)4CH3
Name
Methane
Ethane
Propane
Butane
Pentane
Hexane
C7H16
C8H18
C9H20
C10H22
CH3CH2CH2CH2CH2CH2CH3 or Heptane
CH3(CH2)5CH3
CH3(CH2)6CH3
Octane
CH3(CH2)7CH3
Nonane
CH3(CH2)8CH3
Decane
Introduction
Facts about Organic Compounds:





All contain carbon atoms.
Almost all contain hydrogen atoms.
Many common ones have oxygen, nitrogen, or sulfur atoms.
Most are molecular, few are ionic.
Most carbon-containing compounds are organic compounds. Ex: HCN, H2CO3
Hydrocarbons
Organic compounds consisting only of carbon atoms and hydrogen atoms are called
hydrocarbons. In hydrocarbons, the number of hydrogen atoms increases as the number of
carbon atoms increases in a systematic way.
Prefix: The prefix is used to indicate the side chains, substituents and low priority functional
groups (which are considered as substituents). The prefix may be added immediately before the
root word or before the infix.
The prefixes used for some common side chains and substituents are shown below. (the prefixes
for functional groups are already given)
Side chain or
Substituent
-CH3
-CH2CH3 (or) C2H5
-CH2CH2CH3
Prefix
methyl-
ethyl-
propyl-
isopropyl-CH2CH2CH2CH3
butyl
sec-butyl
(or)
(1-methyl)propyl
isobutyl
(or)
(2-methyl)propyl
tert-butyl
(or)
(1,1dimethyl)ethyl
-X
halo-
-OR
alkoxy-
-NO2
-nitro
Remember that the alkyl groups along with halo, nitro and alkoxy have the same preference.
They have lower priority than double and triple bonds.
Suffixes are divided into two types: Primary suffix and Secondary suffix
Primary suffix: It is used to indicate the degree of saturation or unsaturation in the main chain.
It is added immediately after the root word.
Type of carbon chain
Primary suffix
Saturated (all C-C bonds)
-ane
Unsaturated: one C=C
-ene
Unsaturated: two C=C
-diene
Unsaturated: one C≡C
-yne
Unsaturated: two C≡C
-diyne
Unsaturated: one C=C &
-enyne
one C≡C
Secondary suffix: It is used to indicate the main functional group in the organic compound and
is added immediately after the 1o suffix.
Note: If there are two or more functional groups in a compound, the functional group with higher
priority is to be selected as main functional group, which must be indicated by a secondary
suffix. The remaining functional groups with lower priority are treated as substituents and are
indicated by prefixes.
The suffixes as well as prefixes used for some important functional groups are shown in the
following table in the decreasing order of their priority.
Also note that different suffix is used when carbon atom of the functional group is not part of the
main chain.
Name of
Functional Representation
group
Suffix
Suffix
When
When
carbon of
carbon of
the
the
functional functional
group is
group is
part of the NOT part of
parent
the parent
chain
chain
Prefix
carboxylic
acid
-COOH
-oic acid
-carboxylic
acid
Acid
-oic
anhydride
anyhydride anhydride
Ester
-carboxylic
alkyl -
carboxy-
-
-COOR
alkyl -oate
-COX
-oyl halide
-CONH2
-amide
Nitrile
-CN
-nitrile
Aldehyde
-CHO
-al
Ketone
-CO-
-one
-
oxo-
Alcohol
-OH
-ol
-
hydroxy
Thiol
-SH
-thiol
-
mercapto
Amine
-NH2
-amine
-
amino-
Imine
=NH
-imine
-
imino-
Alkene
C=C
-ene
-
-
Alkyne
C≡C
-yne
-
-
Acid
halide
Acid
amide
Note: This is not the complete reference.
carboxylate
-carbonyl
halide
carboxamide
alkoxycarbonyl-
halocarbonyl-
carbamoyl-
-carbonitrile cyanocarbaldehyde
oxo-
Alkanes are structurally the simplest type of hydrocarbon, consisting of only a single bond
between carbon atoms. The number of hydrogen atoms in an alkane can be calculated using the
given formula:
(# of carbon atoms x2) +2 = # of hydrogen atoms
Alkanes are denoted by the suffix -ane. The prefix varies, dependent on the number of carbon
atoms within the compound. A list of common prefixes, as well as the names for common
alkanes is provided in Table 1.1 below.
Example: C4H10 -> 4 carbon atoms -> but- + -ane = butane
The prefix but- signifies that the molecule consists of four carbon atoms. Combining this with
the suffix -ane, since the molecule is an alkane, yields the name butane.
C9H20 -> 9 carbon atoms -> non- + -ane = nonane
Non-is the prefix used to describe a hydrocarbon with nine carbons. Since single bonds exist
between each carbon atom, the molecule is an alkane, and thus the suffix -ane is used.
Combining together both the prefix and the suffix yields the name nonane.
Likewise, alkenes are hydrocarbons consisting of one or more double bonds. The number of
hydrogen atoms also increases accordingly to the number of carbon atoms, given the equation:
(# of carbon atoms x2) = # of hydrogen atoms
The rules to naming alkenes are the same as that of alkanes, except that alkenes are given the
suffix –ene.
Examples: C2H4 -> 2 carbon atoms -> eth- + -ene = ethene
The prefix eth- signifies that the molecule consists of two carbon atoms. Since the molecule
contains double bonds between carbon atoms, the suffix -ene is used, denotating that the
molecule is an alkene. Thus the molecule is termed ethene.
C8H16 -> 8 carbon atoms -> oct- + -ene = octane
The prefix oct- is used since the molecule consists of eight carbon atoms. Due to the double
bonds between carbon atoms, the suffix -ene is used to denotate that the molecule is a alkene.
Thus the molecule is named octane.
Lastly, alkynes are organic compounds composed of one or more triple bonds. An equation
relating the number of carbon and hydrogen atoms found in an alkyne is given by the formula:
(# of carbon atoms x2) - 2 = # of hydrogen atoms
Alkynes are given the suffix –yne. The rules for naming alkynes are the same to those of alkanes
and alkenes.
Examples: C3H4 -> 3 carbon atoms -> prop- + -yne = propyne
Since the molecule consists of three carbon atoms, the prefix prop- is used. The suffix -yne is
used since the molecule consists of triple bonds between the carbon molecules and is therefore
an alkyne. Thus the molecule is named propyne.
C10H18 -> 10 carbon atoms -> dec- + -yne = decyne
The prefix dec- is used since the molecule contains ten carbon atoms. Due to the triple bond
between carbon atoms, the suffix -yne is used, denotating that the molecule is an alkyne.
Therefore the molecule is termed decyne.
Table 1.1
Number of
Carbon
Atoms
Prefix
Alkanes
Alkenes
Alkynes
CnH2n+2
CnH2n
CnH2n-2
(Single bonds)
(Double bonds)
(Triple bonds)
1
Meth-
Methane
-
-
2
Eth-
Ethane
Ethene
Ethyne
3
Prop-
Propane
Propene
Propyne
4
But-
Butane
Butene
Butyne
5
Pent-
Pentane
Pentene
Pentyne
6
Hex-
Hexane
Hexene
Hexyne
7
Hept-
Heptane
Heptene
Heptyne
8
Oct-
Octane
Octene
Octyne
9
Non-
Nonane
Nonene
Nonyne
10
Dec-
Decane
Decene
Decyne
A cyclo- is a ring of carbon atoms joined up together. Some common cyclo- compounds are
cycloalkanes, cycloalkenes and cycloalkynes. Benzene is one of the most common cycloalkenes.
Below is the structural formula of cyclobutane.
The rules to cyclo- compounds are as simple as any other hydracarbons.
1. Count the longest carbon chain.
2. Identify the bonds between the carbon atoms; single bonds - cycloalkane, double bonds cycloalkene.
3. Use Table 1.1 to after identifying the number of carbon atoms, add the prefix cyclobefore the appropriate name.
C6H6, benzene, is a special alkene with six carbon atoms in the shape of a hexagonal ring.
Molecules with similar structure to benzene make up a large percent of known organic
compounds.
Functional Groups
Carbon atoms tend to form the main framework in organic compounds, the hydrogen atoms in
the chain can be replaced by other atoms or group or atoms to form a whole different compound.
In this formula, two hydrogen atoms in the original butane compound are replaced by one
chlorine atom and one bromine atom. The name of the compounds depends on the location of the
replaced atom. In this case, the chlorine is at the end of the carbon chain, therefore, it is given the
systematic name 1-chloro for the reason that it is attached to the first carbon from one end of the
carbon chain. Bromine is attached to the third carbon atom, so the second part of the name is 3bromo. With four carbon atoms and solely single bonds in this compound, the full name is 1chloro-3-bromobutane.
Functional groups are individual atoms or groupings of more than one atom that attach to the
main carbon chain and give the compound their characteristic properties. Some common
functional groups are hydroxyl group (-OH) and carboxyl group(-COOH). The presence of
functional groups also increases the possibility of isomers. Isomers are molecules that have the
same molecular formula, but a different structural formula. For example, if one of the hydrogen
atoms is replaced by a hydroxyl group in pentane, more than one possibility exists for the point
of attachment of –OH; at the end of the carbon chain or at the middle of it. Either way, the
molecular formula is C5H12O, but the structural formula for the two different possibilities is
different.
Compounds that contain the functional group –OH are generally known as alcohols and are
given the suffix –ol. The simplest alcohol is methanol, CH3OH, in which one of the hydrogen
atoms is replaced by an –OH group. The systematic name methanol comes from methane with
the –e replaced by the designated suffix –ol. However, more complicated compounds require
more indication of the position of the functional group.
Problems
1. Two compounds with the same molecular formula and different structural formula are ______.
2. A special alkene with six carbon atoms in the shape of a hexagonal ring is a ______.
3. What type of hydrocarbon is C3H6?
4.
5.
6.
7.
a. Alkane
b. Alkene
c. Alkine
d. Alkyne
Name the following compound: C9H20
a. Nonane
b. Nonene
c. Nonine
d. Nonyne
Name the following compound: C6H10
a. Hexane
b. Hexene
c. Hexine
d. Hexyne
The molecular formula for butene is _____.
a. C4H10
b. C8H4
c. C4H6
d. C4H8
What is the systematic name for the follow compound?
a.
b.
c.
d.
2- butanol
2- pentane
5- pentanol
1- pentanol
Solutions
1. Isomers
2. Benzene
3. b; There are twice as many hydrogen than carbon atoms, following the formula C nH2n. This
means that the molecule must be an alkene, thus containing double bonds.
4. a; Since there are nine carbon atoms in the molecule, the molecule has the prefix non- (see
Table 1.1). By plugging in the value n=9 into the formula CnH2n+2, it's apparent that the molecule
is an alkane since this yields C9H20, the molecular formula of the given molecule. Thus the suffix
is -ane. Therefore the molecule is named nonane.
5. d; There are six carbon molecules in the atom, thus the molecule has the prefix hex- (see Table
1.1). Plugging the value n=6 into the formula CnH2n-2 yields the molecular formular C6H10 which
indeed matches the formula given. Thus the molecule is an alkyne and ends in the suffix -yne.
Therefore the molecule is name hexyne.
6. d; First look at the prefix but-. Referring to Table 1.1 it's apparent that the molecule contains
four carbons. The suffix of "butene" ends in -ene, therefore implying that the molecule is an
alkene. Plugging n=4 into the formula for an alkene molecule, CnH2n, yields C4H8.
7. d; First count the number of carbon molecules in the molecule. There are five total carbon
molecules thus, by referring to Table 1.1, the molecule begins with the prefix pent-. Next, it's
observed that there's an alcohol group (OH-) attached to the far right carbon atom. An alcohol
group is designated by the suffix -ol. Thus the molecule is propanol. To designate which carbon
the alcohol is attached to, it's standard to designate the carbon number it's attached to. In this case
it would be 1-propanol since the alcohol is attached to the very end or "first" carbon.