Organic Chemistry: Formulas and Hybridization

Organic Chemistry Overview

• Organic chemistry involves studying hydrocarbons and their derivatives.
• Hydrocarbons are compounds made of hydrogen and carbon atoms.
• Derivatives are compounds derived from hydrocarbons via chemical modifications.
• Early organic chemistry believed organic compounds could only be obtained from living organisms.

Representing Organic Compounds

• Organic compounds can be represented in multiple ways.
• Molecular Formula: Indicates the total number of each type of atom in a molecule.
  • Example: C4H10 represents a compound with 4 carbon and 10 hydrogen atoms.
• Condensed Structural Formula: Shows carbon-carbon bonds without explicitly showing carbon-hydrogen bonds.
• Expanded Structural Formula: Shows all bonds between atoms.
• Bond Line Notation: Represents compounds using lines where each corner/end represents a carbon atom.
  • Hydrogen atoms are not explicitly shown in bond line notation.

Hybridization

• Single bond consists of one sigma bond
• Double bond consists of one sigma and one pi bond
• Triple bond consists of one sigma and two pi bonds
• Hybridization is determined by counting sigma bonds and lone pairs around an atom, not pi bonds.

Calculating hybridisation

• sp3 hybridization: one s and three p orbitals. 25% S character
• sp2 hybridization: one s and two p orbitals. 33% S character
• sp hybridization: one s and one p orbitals. 50% S character
• More s character correlates with greater bond strength and shorter bond length.

Important Figures in Organic Chemistry

• Friedrich Wöhler is considered the father of organic chemistry.
• Wöhler synthesized urea (an organic compound) from ammonium cyanate (an inorganic compound).
• The first organic compound was produced artificially was urea.

IUPAC Nomenclature

• IUPAC (International Union of Pure and Applied Chemistry) provides rules for naming organic compounds.
• Components of IUPAC Name:
  • Prefix (substituents, cyclo) + Word Root (carbon chain length)+ Primary Suffix (bond type) + Secondary Suffix (functional group)

Key components of IUPAC names

• Word Root: Indicates the number of carbon atoms in the main chain.
  • meth- (1), eth- (2), prop- (3), but- (4), pent- (5), hex- (6), etc.
• Primary Suffix: Indicates saturation
  • -ane (single bonds), -ene (double bonds), -yne (triple bonds).
• Secondary Suffix: Shows the senior functional group
• Prefix: indicate side chains, extra group (Flouro, Chloro, Bromo, Iodo)

Rules of IUPAC Nomenclature

• Longest Chain Rule: Select the longest continuous carbon chain as the parent chain.
• Numbering: Number the parent chain to give substituents the lowest possible numbers.
• Prioritize functional groups then double/triple bonds, and then substituents.
• If double and triple bonds are at the same position, double bond gets priority.

Degree of Carbon and Hydrogen

• Primary (1°) Carbon: Bonded to one other carbon atom.
• Secondary (2°) Carbon: Bonded to two other carbon atoms.
• Tertiary (3°) Carbon: Bonded to three other carbon atoms.
• Quaternary (4°) Carbon: Bonded to four other carbon atoms.
• The degree of hydrogen is the same as the carbon to which it is attached.

Homologous Series

• Homologous series contain compounds with the same general formula and similar chemical properties and they differ by CH2 group or 14 units.
• Each member differs by a CH2 group or 14 atomic mass units.
• Examples include alkanes, alkenes, and alcohols.

3D Representation of Organic Compounds

• Wedge-Dash Notation: Represents 3D structure on a 2D plane.
• Solid Wedge: Indicates a bond projecting out towards the observer.
• Dashed Wedge: Indicates a bond projecting away from the observer.
• Normal Line: Indicates a bond lying in the plane of the paper.

Isomerism Definition

• Isomers have the same molecular formula but different structural or spatial arrangements.

Types of Isomerism

• Structural Isomerism
  • Same molecular formula, different structure.
  • Types include:
    • Chain Isomerism: Difference in carbon chain size/arrangement.
    • Positional Isomerism: Difference in position of double bond/functional group.
    • Functional Isomerism: Different functional groups.
    • Metamerism: Different alkyl groups around polyvalent functional groups of an ether, etc.
    • Ring-Chain Isomerism: Different arrangement of atoms in a ring vs. chain.

Tautomerism Definition

• Tautomerism is a type of structural isomerism involving the rearrangement of bonds and atoms.

Stereoisomerism Definition

• Stereoisomers: Same molecular formula, same structure different spatial arrangement.

Key concepts for Stereoisomerism:

• Stereoisomerism: different spatial arraignment of atoms
• Constitutional isomers: same molecular formula but different connectivity
• Configurational: Can be separated
• Conformational: Cannot be separated
• Enantiomers: isomers that are mirror images of each other
• Diastereomers: stereoisomers that are not mirror images
• Special Arrangement: Includes diastereomers, geometric isomers (cis/trans).

Naming Conventions

• n- prefix means straight-chain.
• iso- prefix means a methyl group (CH3) on the second carbon atom.
• neo- prefix means two methyl groups on the second carbon atom.
• tert- prefix means a carbon bonded to three other carbons.

Understanding Electronic Effects within Reaction Components

• Substrate: The molecule upon which the reaction occurs.
• Attacking Reagent: Either a nucleophile (electron-rich) or electrophile (electron poor).
• Solvent: A substance used to dissolve reactants.
• Transition State: A temporary, high-energy state during a chemical reaction.
• Intermediate: A molecule formed during a chemical reaction between reactants and product.

Electronic Effects: Permanent & Temporary

• Electronic effects influence electron density in molecules.
• Permanent Effects (e.g., Inductive, Mesomeric, Resonance, Hyperconjugation). They don't need reagent
• Temporary Effects (Electromeric): Require the presence of an attacking reagent.

Inductive Effect (I)

• Permanent effect due to electronegativity differences.
• Distance-dependent.
• Results in partial charges (δ+ or δ-) on atoms in a sigma bond.

How to determine Inductive Effect

• Electron-Donating Groups (+I): Donate electrons, increase electron density.
• Electron-Withdrawing Groups (-I): Withdraw electrons, decrease electron density. Examples: halogens, -NO2, -CN.
• Higher degree carbons are more stable due to +I.

Resonance Effect

• Involves delocalization of pi electrons in conjugated systems.
• Conjugation: Alternating single and multiple bonds.

Rules of Conjugation

• A=B-C⁺, A=B-C:⁻, A=B-C•, A=B-C=D
• Results in resonance structures and a resonance hybrid.

Contributing Factors to Resonance Structures

• Uncharged structures is more stable.
• More covalent bonds lead to greatest stability.
• Negative charge should be on the more electronegative atom and the positive charge should be on the electropositive atom.
• Like charges should be dispersed.

Mesomeric Effect (M)

• Addition of a certain molecule so delocalization can only go in a single location.

Hyperconjugation- Sigmabond delocalization

• Involves delocalization of sigma electrons through empty p-orbitals
• Requires alpha hydrogens (hydrogens on carbons adjacent to a p-orbital- typically around double bonds).
• More alpha hydrogens mean greater stability.

Aromaticity

• Aromatic compounds are cyclic, planar, conjugated, and follow Hückel's rule.
• Hückel's Rule: Aromatic compounds must have (4n + 2) pi electrons.
• Anti-aromatic compounds are cyclic, planar, conjugated, and have 4n pi electrons.
• Non-aromatic compounds lack one or more of these criteria.

Electrophile

• Loves electrons.
• Positively charged.
• Lewis acid.
• Electron deficient and attacks electron-rich centers.
• Neutral of positively charged

Nucleophile

• Loves nucleus.
• Negatively charged.
• Lewis base.
• Electron-rich and attacks electron deficient centers.
• Negative or neutral charged

Common Carbon Intermediates

• Carbocation (positive charge on carbon) — sp2 hybridized, trigonal planar, electron deficient
• A carbanion (negative charge on carbon) is sp3 hybridized, and has a pyramidal shape
• Carbon Free Radical (uncharged carbon with 1 unpaired electron). are formed by homolytic cleavage.

Reactions of Alkanes

• Combustion: Alkanes react with oxygen to form carbon dioxide and water.
• Pyrolysis/Cracking: Thermal decomposition of alkanes into smaller alkanes and alkenes.
• Isomerization: Conversion of straight-chain alkanes to branched isomers.

Reactions of Alkenes

• Addition of hydrogen: Use Ni, Pt, Pd for hydrogenation.
• Addition of X2: X2 adds to the carbons of alkene.
• Addition of HX: Can add to from Markonikov product.
• Addition of H20: H+ and OH group are formed.
• Ozonealysis- O3 bonds to form Ozonide

Markonikov Rule

• With the addition of HX reagents to an alkene, the hydrogen will bond to the carbon with the most number of hydrogens at the carbon chain.

Alkynes

• Have a c triple bond c bond.
• Alkynes have greater s character, stronger and shorter bonds, and are more acidic.
• Can turn into Benzene when ran through hot iron tube.

Qualitative

• Focuses on "what" is in an organic compound.

Quantitative

• Focuses on "how much " is in an organic compound.
• You can determine this by calculating H20 weight.
• You can determine this by calculating Carbon Dioxide weight.

Equations to know

• Carbon % = 12/44 * (mass of CO2/mass of substnace)*100
• Hydrogen % = 2/18 * (mass of HO2/mass of substance)*100
• Nitrogen % = 28/22400 * volume/weight*100
• Sulfur% = 32/233 *(MgSO4/mass of the substance)*100

Key factors in the Boiling point

• BPT directly goes up with molecular mass
• BPT indirectly goes up with more "branching"

Geometric Isomers

• Need different compounds on each end of double bond
• Cis Isomers are adjacent
• Trans Isomers are Diagonal/ Opposite

Chemical Reactivity

• FCLBRIN

How reactions are ordered

1. Sp3
2. Sp2
3. Alkyne