Organic Chemistry Basics: Bonding

Organic Chemistry Basics

Organic chemistry focuses on compounds containing carbon atoms.
Carbon atoms like to form four bonds.
Other elements have their own preferred number of bonds:
- Hydrogen (1st group): 1 bond
- Beryllium (2nd group): 2 bonds
- Boron (3rd group): 3 bonds
- Nitrogen: 3 bonds
- Oxygen: 2 bonds
- Fluorine and other halogens: 1 bond (except for some cases where they can form 7 bonds)

Lewis Structures

Understanding the number of bonds each element likes to form helps in drawing Lewis structures.
Lewis structure of water (H2O):
- Oxygen likes to form 2 bonds and has 2 lone pairs to reach 8 electrons.
- Hydrogen likes to form 1 bond.
Lewis structure of methyl fluoride (CH3F):
- Carbon likes to form 4 bonds.
- Hydrogen likes to form 1 bond.
- Fluorine likes to form 1 bond and has 3 lone pairs.

Bond Types

Covalent bonds:
- Non-polar covalent bonds: electrons are shared equally (e.g., carbon-hydrogen bonds).
- Polar covalent bonds: electrons are shared unequally (e.g., carbon-fluorine bonds).
Hydrogen bonds: special type of polar covalent bond between hydrogen and nitrogen, oxygen, or fluorine.
Ionic bonds: electrons are transferred, not shared.

Alkanes, Alkenes, and Alkynes

Alkanes: saturated organic compounds with single bonds (e.g., methane, ethane, propane).
Alkenes: unsaturated organic compounds with at least one double bond (e.g., ethene, propene).
Alkynes: unsaturated organic compounds with at least one triple bond (e.g., ethyne, propyne).

Bond Length and Strength

Carbon-carbon single bonds are longer than double bonds, which are longer than triple bonds.
Triple bonds are stronger than single bonds, but sigma bonds are stronger than pi bonds.

Hybridization

Hybridization of a carbon atom depends on the number of atoms and lone pairs attached to it:
- Sp3 hybridization: 4 groups (e.g., methane).
- Sp2 hybridization: 3 groups (e.g., ethene).
- Sp hybridization: 2 groups (e.g., ethyne).

Bond Order and Sigma/Pi Bonds

Bond order: the number of bonds between two atoms.
Sigma bonds: single bonds.
Pi bonds: double and triple bonds.

Formal Charge

Formula to calculate formal charge: valence electrons - (number of bonds + dots)
Examples: calculate the formal charge of each carbon atom in three situations.### Formal Charge and Ion Types
Carbon atoms can have formal charges indicating their electron state: cations (+ charge) represent positively charged ions, while anions (- charge) are negatively charged ions.
A carbocation (positively charged carbon) has four valence electrons minus three bonds and one dot (electron), resulting in a formal charge of +1.
A neutral carbon has four valence electrons minus four bonds, yielding a formal charge of 0.
A carbon anion carries a negative charge, calculated as valence electrons (4) minus the sum of bonds (3) plus lone pairs (2 dots totaling 5), resulting in a formal charge of -1.

Radicals

Radicals are species with an odd number of electrons, exemplified by the methyl radical, which is neutral.

Sulfur and Nitrogen Formal Charge Calculation

Sulfur, in group 6A, has six valence electrons. With one bond and three lone pairs (6 dots), the formal charge is -1 (6 - 7).
Nitrogen, in group 5A, has five valence electrons. In the ammonium ion, with four bonds and no dots, the formal charge is +1 (5 - 4).

Electrons Count in Ions

Bonding electrons are the total from bonds (2 electrons per bond), while nonbonding electrons arise from lone pairs (2 electrons per pair).
A structure with four bonds has 8 bonding electrons, while with three lone pairs, it has 6 nonbonding electrons.

Lewis Structures and Functional Groups

Example molecules include CH₃CH₂OH (an alcohol, ethanol) with two carbons and an -OH (alcohol) functional group.
CH₃CHO contains a carbonyl group (C=O) and is classified as an aldehyde (acetaldehyde).
An ether, like CH₃OCH₃ (dimethyl ether), features an oxygen between two carbon atoms.

Ketones, Aldehydes, Esters, and Carboxylic Acids

Ketones have a carbonyl group (C=O) in the middle, such as in propanone.
Aldehydes have a carbonyl group at the end of the carbon chain, with a formula such as CH₃CHO.
Esters have the functional group with a carbonyl and an ether linkage, for example, methyl ethanoate.
Carboxylic acids contain a carbonyl and -OH group (COOH), named according to the length of the carbon chain; pentanoic acid contains five carbons.

Structure Expansion

When expanding structures, place common groups (methyl, carbon, bromine, hydroxyl) accordingly, noting the typical positions of different carbon chains and substituents.
Methyl groups commonly appear at the chain's ends, while the ch2 groups are generally positioned in the middle.

Organic Chemistry Basics

Organic chemistry centers on compounds composed of carbon atoms, known for forming four bonds.
Each element has specific bonding preferences, such as:
- Hydrogen: 1 bond
- Beryllium: 2 bonds
- Boron: 3 bonds
- Nitrogen: 3 bonds
- Oxygen: 2 bonds
- Halogens (including Fluorine): typically 1 bond, but can have expanded valence in rare cases.

Lewis Structures

Knowledge of bonding preferences aids in constructing Lewis structures.
Water (H2O) features oxygen forming 2 bonds with 2 lone pairs, while each hydrogen forms a single bond.
Methyl fluoride (CH3F) has carbon forming 4 bonds, hydrogen 1 bond, and fluorine 1 bond with 3 lone pairs.

Bond Types

Covalent bonds arise from shared electrons, categorized into:
- Non-polar covalent bonds: equal sharing (e.g., C-H).
- Polar covalent bonds: unequal sharing (e.g., C-F).
Hydrogen bonds are a specific type of polar covalent bond involving hydrogen and electronegative elements like N, O, or F.
Ionic bonds occur when electrons are completely transferred between atoms.

Alkanes, Alkenes, and Alkynes

Alkanes are saturated hydrocarbons featuring only single bonds (e.g., methane, ethane, propane).
Alkenes contain at least one double bond (e.g., ethene, propene).
Alkynes include at least one triple bond (e.g., ethyne, propyne).

Bond Length and Strength

Single carbon-carbon bonds are longer than double bonds, which are longer than triple bonds.
Triple bonds exhibit greater strength than single bonds, with sigma bonds being stronger than pi bonds.

Hybridization

Carbon hybridization reflects the group's presence around it:
- Sp3 hybridization for 4 groups (e.g., methane).
- Sp2 hybridization for 3 groups (e.g., ethene).
- Sp hybridization for 2 groups (e.g., ethyne).

Bond Order and Sigma/Pi Bonds

Bond order indicates the total number of bonds between two atoms.
Sigma bonds represent single bonds, while pi bonds involve double and triple bonds.

Formal Charge

Formal charge is calculated as: valence electrons - (number of bonds + unshared electrons).
The process can be practiced with varying carbon atom situations to determine formal charges.

Formal Charge and Ion Types

Carbon can exhibit formal charges indicating electron states:
- Cations: positively charged ions.
- Anions: negatively charged ions.
A carbocation (+1) has 4 valence electrons minus 3 bonds and 1 lone electron.
A neutral carbon has a formal charge of 0.
A carbon anion (-1) has 4 valence electrons minus 3 bonds and 2 lone pairs.

Radicals

Radicals contain an unpaired electron, displayed by the methyl radical, a neutral entity.

Sulfur and Nitrogen Formal Charge Calculation

Sulfur (group 6A) possesses six valence electrons, with a formal charge of -1 when bonded once and having three lone pairs.
Nitrogen (group 5A) has five valence electrons; in the ammonium ion, with four bonds and no lone pairs, the formal charge is +1.

Electrons Count in Ions

Bonding electrons: total from bonds (2 per bond).
Non-bonding electrons: from lone pairs (2 per lone pair).
A molecular structure with four bonds has 8 bonding electrons and three lone pairs results in 6 nonbonding electrons.

Lewis Structures and Functional Groups

Example: Ethanol (CH₃CH₂OH) is an alcohol with two carbons and an -OH functional group.
Acetaldehyde (CH₃CHO) showcases a carbonyl group (C=O) and is classified as an aldehyde.
Dimethyl ether (CH₃OCH₃) is categorized as an ether showcasing an -O- linkage between two carbons.