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.

Learn about the basics of organic chemistry, including the bonding properties of carbon and other elements in compounds.