ORG CHEM | ETA Reviewer

Organic Chemistry

study of carbon-containing compounds that for the most part have a carbon-hydrogen bond

Coining of Organic Chemistry

It was first coined in 1806 by Swedish chemist Jöns Jacob Berzelius, who used it to describe compounds derived from living organisms.

Vitalism

Based on the differences between inorganic and organic compounds, this theory arose stating that life force existed only in organic compounds.

Friedrich Wöhler

He synthesized urea, a compound in urine, from the inorganic silver cyanate with ammonium in 1828. It disproved the theory of vitalism, proving that organic compounds can be synthesized in the lab.

The History of Organic Compound Molecular Structure and Isomerism

August Kekulé, Archibald Couper, and Alexander Butlerov proposed the idea that the tetravalency of carbon allows for the creation of chains and rings, explainign the diversse structures or organic compounds.

The History of Covalent Bonding

Gilbert Lewis introduced the concept of covalent bonds in 1916, while Linus Pauling proposed resonance to explain the stability of certain molecules. At the same time, Sir Christopher Ingold introduced reaction mechanisms to better understand the processes involved in organic reactions.

Organic Compounds

• primary composed of C, bonded to H, O, N, S and other non-metals

• covalent bonding (weaker bond)

• low melting and boiling points due to weaker intermolecular forces like van der Waals interactions or hydrogen bonds

• low conductivity

• non-polar (although compounds with polar groups can dissolve in water)

• vast range of structure

• combustible by reacting with oxygen to produce CO2, water, and heat

• have more varied reactions with acids and bases depending on the included functional groups

Inorganic Compounds

• usually do not have carbons, based on metals, salts, and non-metals

• ionic bonding

• higher melting and boiling points (due to stronger intermolecular forces)

• higher conductivity

• polar

• simpler structure

• non-combustible

• have more predictable reactions with acids and bases

Carbon’s Tetravalency

Because carbon has four valence electrons, it can form many kinds of covalent bonds with a variety of elements

Catenation

ability of carbon atoms to form long chains or rings by bonding with other carbon atoms, forming linear, branched, and ring structures

Bond strength and stability

C-C bond and C-H bond are very stable due to bond energies, making carbon-based compounds stable and durable under various conditions.

Isomerism

same molecular formula can have multiple different structures or arrangements of atoms

Stereoisomers

different spatial arrangement

Hybridization

It allows carbons to form different types of bonds by mixing its s and p orbitals into new hybrid orbitals such as sp, sp² , sp³

sp³ Hybridization

Seen in methane (CH₄), carbon is sp³ hybridized, forming four equivalent tetrahedral bonds.

sp² Hybridization

Seen in ethene (C₂H₄), carbon is sp² hybridized, forming a planar structure with a double bond.

sp Hybridization

Seen in ethyne (C₂H₂), carbon is sp hybridized, forming a linear molecule with a triple bond.

Hydroxyl group

(-OH); found in alcohols

Carbonyl group

(C=O); Found in aldehydes and ketones

Carboxyl Group

(-COOH); Found in carboxylic acids

Amino group

(-NH2); found in amines and amino acids

Pi bonds

bonds formed by the overlap of orbitals in a side-by-side fashion, top bonds in double bonds between carbon atoms

Sigma bonds

bonds formed by the overlap of orbitals in an end-to-end fashion

Bond composition of C=C

one sigma bond and one pi bond

Bond composition of Triple Covalent Bond Between Carbon Atoms

one sigma bond and two pi bonds

Substitution Reactions

One atom or group of atoms is replaced by another (common in alkanes and aromatics).

Addition Reactions

Atoms or groups are added to a double or triple bond (common in alkenes and alkynes).

Elimination Reactions

Atoms or groups are removed, typically leading to the formation of double or triple bonds.

Oxidation-Reduction (Redox) Reactions

Organic compounds can undergo redox reactions where electrons are transferred, particularly involving oxygen or hydrogen atoms.

Hydrocarbons

They are compounds that only contain carbon and hydrogen. It usually has the formula C_xH_y, and they are mostly colorless gases with minimal odors (though they can be solid and liquid).

States of Matter of Hydrocarbons

Small alkanes are gases at room temperature while larger alkanes can be liquids or solids based on the chain length.

Boiling and Melting Points of Hydrocarbons

Alkanes have low boiling and melting points due to weak van der waals forces. However molecular mass increases as boiling points increase. Branched alkanes also have lower boiling points due to decreased surface area and weaker van der Waals interactions.

Combustion

hydrocarbons react with oxygen gas to produce carbon dioxide, water, and energy; usually resulting in a flame

Cracking

Larger hydrocarbons are broken down into smaller, more useful ones through applying heat, pressure, or a catalyst. This is usually used for producing gasoline or diesel.

Carotenes

a hydrocarbon pigment found in plants like carrots and green leaves, they also make up a large percentage of natural rubber.

Alipatic/acyclic Hydrocarbons

straight or branched chains with no rings

Saturated Hydrocarbons

Also known as alkanes, they consist of only single bonds between carbon atoms, which are all sp³ hybridized. They have the simplest structure and are non-reactive under normal conditions. They are usually used as fuel, such as ethane, propane, butane, and methane in natural gas.

Formula of Saturated Hydrocarbons

C_nH_2n+2

Unsaturated Hydrocarbons

They have at least one double or triple bonds. These bonds make them more chemically reactive

Alkenes

The have at least one double bond between carbon atoms, which are sp² hybridized. They are usually used in the creation of plastics, polymers, and rubber, such as ethylene or ethene. Ethene is released by bananas to speed up the ripening process.

General Formula of Alkenes

C_nH_2n

Alkynes

The have at least one triple bond between carbon atoms, which are sp hybridized. They are usually used in metal work and fruit preservation, such as ethyne.

General Formula of Alkynes

C_nH_2n-2

Alicyclic Hydrocarbons

The carbon atoms are arranged in a ring. These are usually used in pharmaceutical engineering.

Homocyclic

The ring is made up of solely carbon atoms

Resonance

a quality some molecules have wherein the electrons are not fixed in a certain location but can move and “spread out” across several atoms, providing stability

Aromatic Compounds

They have alternating single and double bonds, which provide extra stability due to resonance.

Benzene

With the formula C₆H₆, each of the six carbon atoms in the ring have a hydrogen atom attached. It is considered a pollutant and carcinogen.

Cycloalkanes

These are non-aromatic compounds that do not have the resonance structure due to only being made out of single bonds, but still have rings. They have a general formula of C_nH_2n.

Anti-Aromatic

They do not follow the rules of aromaticity and are less stable.

Heterocyclic Hydrocarbons

at least on atom in the ring is not a carbon

Alkanes’ Boiling Points

The boiling point increases with the number of carbon atoms in the chain, as this increases the surface area, leading to stronger intermolecular forces that require more energy to break.

Branching Affecting Alkanes’ Boiling Points

branching lowers the surface area, leading to weaker intermolecular forces, lowering the boiling point.

Alkane’s Melting Points

Melting points follow a similar trend to boiling points that is less predictable due to differences in molecular packing.

Density and Solubility of Alkanes

• the nonpolar nature of alkanes makes them insoluble in water and soluble in organic compounds

• it is less dense than water, ranging from 0.6 to 0.8 g/mL; so it floats in water

State of Matter of Small Alkanes

Compounds with a chain of 1-4 carbons are usually gases

State of Matter of Medium-chain Alkanes

Compounds with a chain of 5-17 carbons are usually liquids

State of Matter of Long-chain Alkanes

Compounds with a chain of at least 18 carbons are usually solids

Fat-soluble Vitamins

• nonpolar due to long hydrocarbon chains, allowing them to dissolve and be stored in fatty tissues and the liver

• they do not need to be consumed as frequently

• toxicity could occur if consumed in excess

• examples include Vitamins A, D, E, and K

Water-soluble Vitamins

• polar due to presence of hydroxyl groups, allowing them to dissolve in water

• they need to be consumed as frequently since they are absorbed quickly and excreted rapidly in urine

• toxicity is not as much of a concern but deficiencies happen more easily

• examples include Vitamins C and B-complex vitamins

Molecular Formula

just shows atoms and number of each kind of atom

Structural Formulas

They show every element as its symbol and every bond as a line, similar to the Lewis Structure without the non-bonding electron pairs. It is best used for small and simple molecules to show the full connectivity.

Condensed Structural Formulas

The bonds to hydrogen atoms are not explicitly shown, making the formula more compact. The carbon atoms are grouped with the hydrogen atoms directly bonded to them.

Line-Bond/Skeletal Structures

Used in the professional field and for more complex structures, they represent the structure using lines, where the carbons are vertices or ends of lines. Bonds to other atoms except hydrogen are still shown.

Structural Isomers

They have the same molecular formula but multiple different connectivity of atoms.

n-Pentane

A straight-chain with a boiling point of 36 degrees.

Isopentane

A branched structure with a boiling point of 28 degrees.

Neopentane

Has a boiling point of 9.5 degrees

Carbon in Bonding

It is tetravalent. It can form four single bonds, two single binds and a double bond, and one single bond and a triple bond.

Hydrogen in Bonding

It is monovalent, meaning it can only form one bond.

Oxygen in Bonding (Neutral)

It has two bond and two lone pairs in compounds like water or alcohol.

Oxygen in Bonding (Negative Formal Charge)

It forms one bond and three lone pairs in compounds such as hydroxide ion.

Oxygen in Bonding (Positive Formal Charge)

It forms three bonds and one lone pair in compounds such as hydronium ion.

Nitrogen in Bonding

It trivalent. It typically forms three bonds and has one lone pair. It carries a positive formal charge with four bonds.

Halogens in Bonding

Fluorine (F), Chlorine (Cl), Bromine (Br), and Iodine (I) usually form one bond and have three lone pairs. They are usually seen in laboratory and medical contexts.

Sulfur in Bonding

It forms two bonds and behaves similarly to oxygen.

Phosphorus

They are usually in phosphate groups and can form five bonds since it can expand its valence shell.

Steps for Drawing Acyclic Alkanes

1. Determine the number of carbon atoms in the alkane.

2. Draw a chain of single bonds between carbon atoms.

3. Attach the correct number of hydrogen atoms to each carbon atom, ensuring that each carbon has four bonds in total.

Drawing Cycloalkane

1. Determine the number of carbon atoms in the ring.

2. Draw a polygon representing the carbon ring (e.g., a triangle for cyclopropane or a hexagon for cyclohexane).

3. Attach the appropriate number of hydrogen atoms to each carbon.

Naming Straight-chain Alkanes

prefix based on no. of C atoms in the longest continuous chain + -ane

Prefix for 1 carbon atom/substituent

meth-

Prefix for 2 carbon atoms/substituents

eth-

Prefix for 3 carbon atoms/substituents

prop-

Prefix for 4 carbon atoms/substituents

but-

Prefix for 5 carbon atoms/substituents

pent-

Prefix for 6 carbon atoms/substituents

hex-

Prefix for 7 carbon atoms/substituents

hept-

Prefix for 8 carbon atoms/substituents

oct-

Prefix for 9 carbon atoms/substituents

non-

Prefix for 10 carbon atoms/substituents

dec-

Steps for Naming Acyclic Branched Alkanes

1. Identify the longest carbon chain.

2. Identify the substituents or branches.

3. Number the carbon atoms in the main chain.

4. Assemble the name.

Identifying the substituents (Alkanes)

These are any branches seen in the structure. They are named based on the number of carbon atoms in one branch. The nomenclature follows the assigned prefixes per number of carbons with an added suffix -yl.

Numbering the carbon atoms (Alkanes)

The numbering must start from the end that is closest to a substituent. If there is an equal distance, then the end nearest to the substituent with more carbons is where you start.

Naming for Multiple Substituents (Alkanes)

If there are multiple identical substituents, use prefixes like “di-”, “tri-”, “tetra-”. When writing the position numbers per branch, write one number per branch and separate the numbers with a comma. (e.g. 2,2-methyl-)

Assembling the Name

• For each substituent number, combine the position number/s with the substituent.

• List them alphabetically, ignoring di-,tri-,tert- etc., for identical substituents.

• Add the base name at the end.

• Separate the (group of) position numbers and substituents with a dash. Do not put a dash between the last substituent and the base name. (e.g. 5-ethyl-3-methyloctane)

Steps in Naming Cycloalkanes

1. Determine the Ring Size.

2. Identify the Substituents.

3. Number the Carbon Atoms in the Ring.

4. Assemble the Name.

Determining the Ring size (Cycloalkanes)

Base this on the number of atoms. This follow the same naming conventions for an acyclic alkane with an added cyclo- prefix before it.

Identifying Substituents (Cycloalkanes)

Identify and name the substituents attached to each carbon in the ring.

Number the Carbon Atoms in the Ring (Cycloalkanes)

Start numbering at the carbon with the substituent that is alphabetically first. Then, continue numbering counterclockwise.

Alphabetical Order of the Branches

butyl (4), decyl (10), ethyl (2), heptyl (7), hexyl (6), methyl (1), nonyl (9), octyl (8), pentyl (5), propyl (3)