Organic compound is a compound in which one or more atoms of carbon are covalently linked to atoms of other elements, most commonly hydrogen, oxygen, or nitrogen.
The Carbon Atom
Carbon is a nonmetallic tetravalent element making four electrons available to form covalent chemical bonds. Carbon is the only element that can form so many different compounds because each carbon atom can form four chemical bonds to other atoms. This makes carbon unique among the other elements.
Reasons for having many carbon compounds:
• carbon has the ability to form long carbon-to-carbon chains
• carbon atoms can bind to each other not only in straight chains but in complex branchings
• carbon atoms can share electrons to form single, double or triple bond
• with same collection of carbon atoms and bonds, isomers can be formed
• all of the electrons that are not being used to bond carbon atoms together into chains and rings can be used to form bonds with atoms of several other elements
Bonding Patterns in Hydrocarbons
Hydrocarbons are molecules that contain only carbon and hydrogen. Due to carbon's unique bonding patterns, hydrocarbons can have single, double, or triple bonds between the carbon atoms. The bonding of hydrocarbons allows them to form rings or chains.
Hydrocarbons are classified as either aliphatic or aromatic . Aliphatic described hydrocarbons derived by chemical degradation of fats or oils. Aromatic hydrocarbons described hydrocarbons derived by chemical degradation of certain pleasant-smelling plant extracts. Aliphatic hydrocarbons are divided into alkanes, alkenes, and alkynes. Alkanes have only single bonds, alkenes contain a carbon-carbon double bond, and alkynes contain a carbon-carbon triple bond. Aromatic hydrocarbons are those that are significantly more stable than their Lewis structures would suggest; i.e., they possess “special stability.” They are classified as either arenes, which contain a benzene ring as a structural unit, or nonbenzenoid aromatic hydrocarbons, which possess special stability but lack a benzene ring as a structural unit.
Illustration: H H
Alkane : Ethane H-C – C- H with single bond between C atoms
H H
Alkene: Ethene H H with double bond between C atoms
C=C
H H
Alkyne: Ethyne H – C = C- H with triple bond between C toms
Naming of Hydrocarbon
Some Prefixes Used in Naming Aliphatic Hydrocarbon:
Number of C Prefix Number of C Prefix
1 meth- 6 hex-
2 eth- 7 hept-
3 prop- 8 oct-
4 but- 9 non-
5 pent- 10 dec-
Naming of Hydrocarbon
I. Alkane: prefix + ane
Example : 5-carbon alkane : pentane
II. Alkene: prefix + ene
Example: 5-carbon alkene: pentene
III.Alkyne: prefix + yne
Example: 5-carbon alkyne: pentyne
Naming of of Cycloalkanne
Example 1: cyclo + name of alkane
H H
C Name: cyclopropane
H - C C - H
H H
Alkyl
It is an alkane minus one hydrogen. In naming alkyl, replace -ane with –yl of the alkane’s name.
Example: alkane alkane structure alkyl alkyl structure
H H
methane H – C – H methyl H – C - H H
IUPAC Rules for Alkane Nomenclature
1. Find and name the longest continuous carbon chain.
2. Identify and name groups attached to this chain.
3. Number the chain consecutively, starting at the end nearest a substituent
group.
4. Designate the location of each substituent group by an appropriate number
and name.
5. Assemble the name, listing groups in alphabetical order. The prefixes di, tri,
tetra etc., used to designate several groups of the same kind, are not
considered when alphabetizing.
Illustration: Name the following organic compound represented by dot-line structure.
A. 4 2
5 3 1 answer: 2-methylpentane
Cl
B. 6 4 2
5 3 1 answer: 3-chloro-2,4 -dimethylhexane
IUPAC Rules for Alkene and Alkyne Nomenclature
1. Identify the longest carbon chain that contains both carbons of the double or triple
bond.
2. The carbon backbone is numbered from the end that yields the lowest positioning for
the double or triple bond.
3. Substituents are added to the name as prefixes to the longest chain.
4. The position of the double or triple bond is indicated using the position of the carbon in
the bond with the lower backbone number, and the suffix for the compound is
changed to “-ene” for an alkene and “-yne” for an alkyne.
Illustration 1: Name the following organic compound:
Solution:
Assign the lowest number to the double bond
5 3 1
4 2 answer: 2-pentene
Illustration 2: Name the following organic compound
answer: 4-chloro-6-diiodo-7-methyl-2-nonyne
When there are two double or triple bonds in the molecule, find the longest carbon chain including both the triple bonds. Number the longest chain starting at the end closest to the double or triple bond that appears first. The suffix that would be used to name this molecule would be - diene for 2 double bond and –diyne for two triple bonds. For example:
1 3 5 7
name: 4-methyl-1,4-octadiyne
2 4 6 8
Lesson 9.4 Sigma Bond and Pi Bond
Sigma bond is a covalent bond resulting from the formation of a molecular orbital by the end-to-end overlap of atomic orbitals Denoted by the symbol σ.
Pi bond is a covalent bond resulting from the formation of a molecular orbital by side-to-side overlap of atomic orbitals along a plane perpendicular to a line connecting the nuclei of the atoms. Denoted by the symbol π.
Locating σ and π bond
σ - bonds
C C C C C C
π - bonds
Example: How many sigma and pi bonds are there in ethene ?
Hybridization
Hybridization is the fusion of atomic orbitals to form newly hybridized orbitals, which in turn, influences molecular geometry and bonding properties. Hybridization is also an expansion of the valence bond theory. Three types of hydrocarbon compounds will be utilized to illustrate sp3, sp2, and sp hybridization.
Hybridization of Ethane
Ethane is a two carbon molecule with a single-bond between the two carbons To understand the hybridization, consider the orbital diagram of the unhybridized valence electrons of unhybridized carbon.
Carbon has four valence electrons, two in the 2s orbital and two more in three 2p orbitals In ethane molecule, carbon needs to make four single bonds, one to the other carbon atom and three more to the hydrogen atoms. Single bonds can only be made with s-orbitals or hybrid orbitals, and as it stands carbon can not make four bonds. To rectify this the atomic orbitals go through a mixing process called hybridization, where the one 2s and the three 2p orbitals are mixed together to make four equivalent sp3hybrid orbitals . One s orbital and 3 p-orbitals were used in this case, and the result is a total of four sp3 hybrids. The four electrons are then distributed equally among them.
There are two types of orbitals with two types of shapes. A s type orbital is a sphere of electron density around an atom. Hybrids and sorbitals can make sigma type bonds where the electron density is shared directly between the atoms. The other type, p-orbitals, have two lobes above and below the plane of the atom. They are used to make π bonds, which make up double and triple bonds.
sp3 hyrbid orbital
Shown above is the sp3 orbital used by the carbon to make the sigma bond with the adjacent carbon. There are three things to notice:
1) The bulk of the electron density is directly between the two carbon atoms, indicative of a sigma bond.
2) The shape of the hybrid matches what orbitals were used to make it. For this case, sp3 hybrids are 3 parts p orbitals and 1 part s orbital. The end result is an orbital that is mostly p shaped but it a little bit lop-sided.
3) sp3 hybrids take a tetrahedral geometry with an angle between them of 109.5 degrees. Click on one of the ethane pictures above and rotate the 3D image until you can see this geometry.
Hybridization of Ethylene
Unlike methane, ethylene is shaped differently, despite the fact that the carbon in ethylene has the same electron configuration. Evidence shows that the carbon in an ethylene molecule is sp2 hybridized. This means that 1 s orbital is being mixed with 2 p orbitals.
The energy diagram setup this time is different because only 2 p orbitals are being mixed. While creating the energy diagram, be sure not to make mistake as shown at the above right figure. By placing two electrons in the same orbital, Hund's rule is violated. The said rule states that all orbitals among the same energy levels have to be filled with at least one electron before being paired up again. The 2p orbital here is considered low enough energy to be classified within the same energy level as the sp2 orbitals. The figure below portrays the correct way to distribute your electrons.
Notice how that lone electron in the 2p orbital is separate from the electrons in the sp2 orbitals. This is what influence ethylene's shape. The lone electron from each carbon will remain in its respective p orbital and form a pi bond with the other p orbital electron. Thus, ethylene is a planar molecule, with orbitals spaced 120 degree angles apart.
Hybridization of Acetylene ( or ethyne )
Acetylene is an sp molecule. This means that 1 s orbital is being mixed with 1 p orbital. The energy diagram for this setup is shown below::
The lone electrons in the 2p orbitals are not part of the sp orbitals. Instead, each electron is in its respective p orbital, and will bond with its respective p orbital of the other carbon. This in itself will create a sigma bond and two pi bonds, leading to the formation of a linear molecule.
In Lewis structure, acetylene is comprised of 2 triple-bond carbons. The bond angle is 180 degrees, indicative of a linear molecule.
Organic Compounds : Carbon Atom, Hydrocarbons Bonding & Naming, Sigma & Pi bonds , and Hybridization
Functional Groups - Naming, Properties and Reactivities
A functional group is a group of atoms within a compound that is responsible for the characteristic chemical reactions of that compound. Functional groups also play an important part in organic compound nomenclature - combining the names of the functional groups with the names of the parent alkanes provides a way to distinguish compounds.
Some Common Functional Groups:
I. Alcohols
Alcohols are functional groups characterized by the presence of an -OH group. The general formula for alcohol is : R – OH where R is an alkyl . Compared to their parent alkanes, alcohols have higher boiling points. They are polar in nature caused by the difference in electronegativities between carbon and the oxygen atoms. In a reaction, alcohols cannot leave the molecule by themselves. To leave a molecule, they must be protonated to water. In the presence of a strong base, alcohols can be deprotonated.
Nomenclature of Alcohols
In naming alcohol, the terminal “-e” of the parent carbon chain (alkane, alkene, or alkyne) is dropped and the addition of “-ol” as the ending.
Example: CH3CH2- + OH CH3CH2-OH
ethyl + OH ethanol ( or ethyl alcohol )
Alcohols are used in beverages, antifreeze, antiseptics, and fuels. They are also used as preservatives for specimens in science, and they are used as reagents and solvents in industries because they can dissolve both polar and non-polar substances.
II. Ethers
Ethers are organic compounds that contain an ether group. An ether group is an oxygen atom connected to two alkyl or aryl groups. They follow the general formula R-O-R’ ( R is a substituent that can be the same or not ). The C-O-C linkage is characterized by bond angles of 104.5 degrees, with the C-O distances being about 140 pm. The oxygen of the ether is more electronegative than the carbons. Thus, the alpha hydrogens are more acidic than in regular hydrocarbon chains.
Ethers are nonpolar due to the presence of an alkyl group on either side of the central oxygen. The oxygen atom is unable to participate in hydrogen bonding due to the presence of alkyl groups on its side. Ethers have lower boiling points . However, as the alkyl chain of the ethers becomes longer, the difference in boiling points becomes smaller. This is due to the effect of increased Van der Waals interactions as the number of carbons increases, and therefore the number of electrons increases as well. The two lone pairs of electrons present on the oxygen atoms make it possible for ethers to form hydrogen bonds with water. Ethers are more polar than alkenes, but not as polar as esters, alcohols or amides of comparable structures.
Ethers have relatively low chemical reactivity. They resist undergoing hydrolysis. Ethers form peroxides in the presence of oxygen or air.
Nomenclature of Ethers
In naming , identify the alkyl groups on either side of the oxygen atom in alphabetical order, then write “ether.”
Examples: a) CH3 – O – CH2CH3 ethyl methyl ether
b) CH3 – O – CH3 dimethyl ether
Note: If the two alkyl groups are identical, the ether is called di[alkyl] ether.
III. Ketones
Ketone is an organic compound containing an oxygen atom joined to a carbon atom by a double bond. In ketone, the carbonyl functional group ( C=O ) is placed within a molecule. Its general structure is : O where R and R’ can be
R – C – R’
a variety of carbon-containing substituents.
Ketones are polar due to the carbonyl group and can interact with other compounds through hydrogen bonding. This hydrogen bonding makes ketones more soluble in water . Ketones are not hydrogen bond donors and they exhibit intermolecular attractions with other ketones. Because of this, ketones are often more volatile than alcohols and carboxylic acids of comparable molecular weights.
Nomenclature of Ketones
Naming of ketone is done by changing the suffix of the parent carbon molecule to “-one.” If the position of the ketone must be specified, parent chain is numbered by giving the lowest number to the carbonyl ( C=O ).
Example: CH2CH3
CH3 – C – C – CH3 3-ethyl-3-methyl -2- butanone
4 3 2 1
O
CH3
IV. Aldehydes
An aldehyde is an organic compound that contains a carbonyl group ( C=O ) with the central carbon bonded to a hydrogen and R group (R-CHO). In aldehydes, the carbonyl is placed at the end of the carbon skeleton rather than between two carbon atoms of the backbone ( just like in ketone ). Like ketones, aldehydes are sp2 hybridized.
Nomenclature of Aldehydes
Aldehydes are named by dropping the suffix “e” of the parent alkane, and adding the suffix “-al”.
Example: aldehyde with 2 C atoms
H
CH3C =O ethanal
Ketones and aldehydes can be readily reduced to alcohols in the presence of a strong reducing agent such as sodium borohydride. In the presence of strong oxidizing agents, they can be oxidized to carboxylic acids.
V. Carboxylic Acids
Carboxylic acids are organic acids that contain a carbon atom that participates in both a hydroxyl and a carbonyl functional group. Its general formula is : R-COOH.
A carboxyl group (COOH) is a functional group consisting of a carbonyl group (C=O) with a hydroxyl group (O-H) attached to the same carbon atom. Carboxyl groups have the formula O . It is usually written as – COOH. Carboxylic acids are
- C – OH
characterized by the presence of one carboxyl group. Since carboxylic acids contain both hydroxyl and carbonyl functional groups, they participate in hydrogen bonding as both hydrogen acceptors and hydrogen donors. Carboxylic acids increase stabilization of non-polar compounds and elevate their boiling points.
Nomenclature of Carboxylic Acids
For IUPAC nomenclature, the suffix “e” of the parent alkane is dropped and the suffix “-oic acid” is added.
O
Example: CH3 – C – OH ethanoic acid
Carboxylic acids are used as precursors to form other compounds such as esters, aldehydes, and ketones.
Carboxylic acids are used in the production of polymers, pharmaceuticals, solvents, and food additives. Carboxylic acids are generally produced from oxidation of aldehydes and hydrocarbons, and base catalyzed dehydrogenation of alcohols.
VI. Esters
Esters are functional groups produced from the condensation of an alcohol with a carboxylic acid. The general formula is: O
R – C – OR’
R and R’ are both alkyl groups. Esters are derivative of carboxylic acids where the hydroxyl (OH) group has been replaced by an alkoxy (O-R) group. They are commonly synthesized from the condensation of a carboxylic acid with an alcohol.
Esters are more polar than ethers, but less than alcohols. They participate in hydrogen bonds as hydrogen bond acceptors, but cannot act as hydrogen bond donors. Esters are more volatile than carboxylic acids of similar molecular weight.
Esters are everywhere. Most naturally occurring fats and oils are the fatty acid esters of glycerol. Esters are fragrant, and those with low molecular weights are commonly used as perfumes and are found in essential oils and pheromones. Polymerized esters, or polyesters, are important plastics.
Nomenclature of Esters
Ester names are derived from the parent alcohol and acid. For example, the ester formed by ethanol and ethanoic acid is known as ethyl ethanoate; “ethanol” is reduced to “ethyl,” while “ethanoic acid” is reduced to “ethanoate.”
O O
Illustration: CH3 – C – OH + CH3CH2 – OH CH3-CO-CH2CH3
ethanoic acid ethanol ethyl ethanoate
VII. Amines
Amines are compounds characterized by the presence of a nitrogen atom, a lone pair of electrons, and three substituents ( R ). The general formula for amines is N-R3. R can be H ( hydrogen ) or alkyl groups. Amines are basic compounds due to the lone pair of electrons. Amines have an unpleasant odor
Amine compounds can hydrogen bond, which affords them solubility in water and elevated boiling points. Amines are reactive due to their basicity as well as their nucleophilicity. Most primary amines are good ligands and react with metal ions to yield coordination complexes
Amines are starting materials for dyes and models for drug design. Amines are also used for gas treatment in the removal CO2 from combustion gases.
Nomenclature of Amines
In naming an amine compound, the prefix “amino-” or the suffix “-amine” is used.
For organic compound with multiple amino groups, the prefixes di, tri, tetr , etc. are used.
. .
Examples: a) CH3 – N – CH3 trimethylamine
CH3
. .
b) CH3CH2 – N – H ethanamine or ethyl amine
H
VIII. Amides
Amides are organic compounds containing nitrogen and has the general formula ; O
RC – NH2
The – NH2 group is directly attached to the carbonyl group ( C=O ).
Amide groups are found in nylon, silk, and wool. Amide is also present in insect repellant. Amides are used widely as color in crayons, pencils and inks, paper industry , plastic and rubber industry, and water and sewage treatment.
Nomenclature of Amide
In naming an amide compound, the suffix “e” of the parent alkane is replaced with the suffix “amide.
O
Example: CH3CH2CH2CH2C – NH2 pentanamide
IX. Alkyl halides
Alkyl halides are organic compounds containing halogens ( fluorine, chlorine, bromine or iodine ). Alkyl halide is formed by replacing one or more hydrogen atoms in an alkane with halogen atoms.They are also known as haloalkanes. Alkyl halides have the following general formula:
Primary alkyl halide : R – CH2 – X
Secondary alkyl halide: R – CH – R
X
R
Tertiary alkyl halide : R – C –R
X
where X is any halogen mentioned above.
Halogen imparts reactivity to alkyl halides. Alkanes impart odorlessness and colorlessness to alkyl halides. Some alkyl halides are less toxic and have high heat of vaporization. They are water-phobic ( they repel water) . Halogenated hydrocarbons are soluble in organic solvents. Some of the haloalkanes do not conduct electricity. Alkyl halides have higher boiling and melting point unlike alkanes. Haloalkanes are less flammable as compared to its component alkanes. Alkyl halides have stronger intermolecular forces (dipole-dipole interaction.)
Nomenclature of alkyl halides
In naming alkyl halides, the name of the alkyl residue is followed by the name of the halide. Examples are methyl iodide and ethyl chloride.
The IUPAC nomenclature considers an alkyl halide a substituted alkane . The name of the halogen is followed by the name of the alkane. Examples are iodomethane and chloromethane. . If an alkyl halide contains more than one halogen, the halogen names are noted in alphabetical order, such as 1-chloro-2-iodobutane.
Illustrations:
a) CH3 – Cl methyl chloride or chloromethane
b) CH3-CH2-F ethyl fluoride or fluoroehtane
c) CH3-CH-CH3 isopropyl iodide or 2-iodopropane
I
d) CH3-CH2-CH-CH3 sec-butyl bromide or 2-bromobutane
Br
e) CH3
H3C - C – CH3 tert-butyl bromide or 2-bromo-2-methylpropane
Br
Alkyl halides are used in labs as synthetic intermediate compounds. They are used as cleansers for cleaning. Commercial uses of haloalkanes include its use in fire extinguishers. Carbon tetrachloride is used to detect neutrinos.
The Four Models of the Atom
