Module 3

• A functional group is a group of atoms within a molecule that has a characteristic chemical behavior
• A functional group is the reactive part of the molecule.
• Organic molecules may have these structural features as well:

  • HETEROATOMS: Atoms other than carbon or hydrogen. Common heteroatoms are nitrogen, oxygen, sulfur, phosphorus, and the halogens.
  • π Bonds. The most common π bonds occur in C=C and C=O double bonds.
• Types of Functional Groups

  1. Functional Groups with Carbon–Carbon Multiple Bonds
  2. Functional Groups with Carbon Singly Bonded to an Electronegative Atom
  3. Functional Groups with a Carbon–Oxygen Double Bond (Carbonyl Groups)
• Functional Groups with Carbon–Carbon Multiple Bonds:

  Hydrocarbons are compounds made up of only the elements carbon and hydrogen.

  • Aliphatic: Alkanes, Alkenes, Alkynes
  • Aromatic: Arenes
• Functional Groups with Carbon–Carbon Multiple Bonds:

  Carbon atoms in alkanes and other organic compounds are classified by the number of other carbons directly bonded to them.

  • A primary carbon (1˚ carbon) is bonded to one other C atom.
  • A secondary carbon (2˚ carbon) is bonded to two other C atoms.
  • A tertiary carbon (3˚ carbon) is bonded to three other C atoms.
  • A quaternary carbon (4˚ carbon) is bonded to four other C atoms.
• Functional Groups with Carbon–Carbon Multiple Bonds:

  
  

  Hydrogen atoms are classified as primary (1°), secondary (2°), or tertiary (3°) depending on the type of carbon atom to which they are bonded

  • A primary hydrogen (1˚H) is on a C bonded to one other C atom.
  • A secondary hydrogen (2˚ H) is on a C bonded to two other C atoms.
  • A tertiary hydrogen (3˚ H) is on a C bonded to three other C atoms.
• Functional Groups with Carbon Singly Bonded to an Electronegative Atom (C-Z σ bond)

  • The electronegative heteroatom Z creates a polar bond, making carbon electron deficient. The lone pairs on Z are available for reaction with protons and other electrophiles, especially when Z = N or O.
• Functional Groups with Carbon Singly Bonded to an Electronegative Atom (C-Z σ bond):

  • Alkyl halides and Amines are classified as 1°, 2°, or 3°
• Functional Groups with a Carbon–Oxygen Double Bond (Carbonyl Groups):

  • The polar C=O bond makes the carbonyl carbon an electrophile, while the lone pairs on O allow it to react as a nucleophile and base.
  • The carbonyl group also contains a π bond that is more easily broken than a C=O σ bond.
• Importance of Functional Groups

  1. Bonding and Shape
  2. Nomenclature
  3. Physical Properties
  4. Chemical Reactivity
  5. Type and Strength of Intermolecular Forces
• Intermolecular Forces

  • The physical properties of a compound are determined by the attractive forces between the individual molecules, called intermolecular forces.
• All intermolecular forces are electrostatic:

  • London dispersion (van der Waals forces)
  • Dipole-dipole interaction
  • Hydrogen bonding
• Ion-ion interactions (forces):

  • Na+ Cl- (oppositely charged particles): extremely strong electrostatic interactions.
  • Much stronger than the intermolecular forces in covalent molecules.
• London dispersion (fleeting dipole-dipole)

  • London dispersion forces are attractions between an instantaneous dipole and an induced dipole.
  • These forces are present in all molecules, whether they are polar or nonpolar. The tendency of an electron cloud to distort in this way is called polarizability.
• Dipole-dipole forces

  • The positive end of one is attracted to the negative end of the other and vice-versa (e.g., H2S, CH3Cl)
• Hydrogen bonding

  • Type of dipole-dipole interactions experienced when H atom is bonded to N, O, or F atom (e.g., H2O, NH3 , HF).
• Physical Properties:

  As the polarity of a molecule increases, the strength of its intermolecular forces increases. This affects the physical properties of molecules.

  • BOILING POINT
  • MELTING POINT
  • SOLUBILITY
• intermolecular forces

  london dispersion forces < dipole-dipole forces < hydrogen bonding
• Boiling point:

  • The larger the surface area, the higher the bp.
  • The more polarizable the atoms, the higher the bp
• The boiling point (bp) of a compound is the temperature at which the liquid form of the compound becomes a gas (vaporizes). In order for a compound to vaporize, the forces that hold the individual molecules close to each other in the liquid must be overcome.
• Melting point:

  • The stronger the intermolecular forces, the higher the mp.
  • The more compact and symmetrical the shape (a crystalline lactice), the higher the mp.
• The melting point (mp) is the temperature at which a solid is converted to its liquid phase. In melting, energy is needed to overcome the attractive forces in the more ordered crystalline solid.
• Solubility is the extent of solute dissolution in a solvent.

  • The nonpolar part of a molecule that is not attracted to H2O is said to be hydrophobic
  • the polar part of a molecule that can hydrogen bond to H2O is said to be hydrophilic
• Soap molecules have two distinct parts:

  • Hydrophilic polar head
  • Hydrophobic nonpolar tail
• Solubility:

  Rule of the thumb: “Like dissolves like”

  • Water: Organic compounds are only soluble in water if it contains one polar functional groups (– O or –N containing functional groups) that can form H-bonding every 5 C atoms.
  • Organic Solvents: Almost all organic compounds are soluble in nonpolar organic solvents
• Application

  • Vitamins are organic compounds needed in small amount for normal cell function.
• Application:

  • Structure of Cell Membrane
• Kinds of Organic Reactions:

  Organic chemical reactions can be organized broadly in two ways:

  • by WHAT kinds of reactions occur and
  • by HOW those reactions occur
• What kinds of reactions do exist?

  • Addition Reaction
  • Elimination Reaction
  • Substitution Reaction
  • Rearrangement Reaction
• Addition reactions occur when two reactants add together to form a single product with no atoms “left over."
• Elimination reaction is, in a sense, the opposite of addition reaction. It occurs when a single reactant splits into two products, often with formation of a small molecule such as water or HX .
• Addition and elimination reactions are exactly opposite.
• A pi bond is formed in elimination reactions, whereas a pi bond is broken in addition reactions
• Substitution reaction occurs when two reactants exchange parts to give two new products
• Rearrangement reaction - Atoms are rearranged resulting in the formation of a new substance or substances.
• How do organic reactions occur?

  Reaction Mechanism is the overall description of how a reaction occur. A complete mechanism accounts for all reactants used and all products formed. It describes in detail exactly what takes place at each stage of a chemical transformation:

  • which bonds are broken and in what order,
  • which bonds are formed and in what order,
  • what the relative rates of the steps are.
• The reactivity of organic molecules is influenced by two main factors:

  • Electron-deficient sites
  • Electron-rich sites
• Bond breaking and Bond making

  • Electrons move from a nucleophilic source (Nu: or Nu:+) to an electrophilic site (E or E+)
  • The nucleophile can be either negatively charged or neutral.
  • The electrophile can be either positively charged or neutral.
  • The octet rule must be followed.
• Bond breaking and Bond making:

  [1] One-step/concerted reaction: involves only one step the starting material is directly converted to a product no matter how many bonds are broken or formed

  [2] Stepwise reaction: involves more than one step the starting material is first converted to an unstable intermediate then goes on to form the product.