Organic chemistry

• Valence electrons: Electrons in the valence (outermost) shell of an atom.
• Valence shell: The outermost electron shell of an atom.
• Electronegativities increase from left to right on the periodic table and decrease from top to bottom within a group.
• Non-polar covalent bonds: Electrons are shared equally and the difference in electronegativity is less than 0.5.
• Polar covalent bonds: Electrons are shared unequally and the difference in electronegativity is between 0.5 and 1.9.

  ~More electronegative= greater fraction of electrons= partial negative charge.

  ~Less electronegative= lesser fraction of electrons= partial positive charge.
• An atom surrounded by four different regions of electrons will be sp3 hybridised and have a tetrahedral geometry; approximately 109*.
• An atom with electrons in three regions will be sp2 hybridised and have a trigonal geometry; approximately 120*.
• An atom with electrons in two regions will be sp hybridised and have a linear geometry; approx 180*. The unhybridised 2p atomic orbitals are perpendicular to each other and to the axis of the two sp hybrid orbitals.
• P-orbitals lined up side by side are pi orbitals while orbitals pointing at each other are sigma orbitals.
• Hybridisation refers to atoms and orbitals, not bonds.
• Hydrogen bond interactions is increased melting points, boiling points, and water solubility.
• Each colour has a different frequency, that corresponds to a different energy. E= hv
• Ionisation energy: The energy required to remove one electron from an atom in its ground state.
• Orbital: A region of space where there is a 95% probability of finding the electron.
• A node represents a zero probability of finding the electron in that region of space and also the point were the wave function changes its phase.
• The higher the number of nodes, the higher the energy of the orbital.
• The principal quantum number: n

  ~The energy of the orbital.
• The angular momentum quantum number: l

  ~Shape of the orbital.
• Magnetic quantum number: ml

  ~Orientation in space of the orbital.
• Pauli Exclusion Principle: Two electrons can occupy the same orbital only if their spins are paired.
• Spin angular momentum quantum number: ms.

  ~The spin of the electron around its own axis.
• Aufbau principle: in ground state atoms and ions, electrons fill the orbitals starting with the lowest energy ones.
• Electrons on a higher energy orbital are more energetic and more reactive.
• Moving across the period there is an increase in electronegativity, they are more positive so increased stability of electrons on the external shell, making them less reactive.

  
  

  ~The energy of p orbitals is lower in fluorine than carbon.
• Molecular orbitals are the result of the linear combination of atomic orbitals.
• Adding electrons to an anti bonding orbital will always weaken or break the bond.
• p orbitals can interact "head-on" with p or s orbitals to from sigma bonds.
• Hybrid atomic orbitals (e.g. sp3) atomic orbitals can also interact "head-on" to form sigma bonds.
• p orbitals can interact "side-on" with other p orbitals to form pi bonds.
• Curved arrows are used to represent the interaction between frontier orbitals.
• Electrons on orbitals centred on more electronegative atoms are LESS nucleophilic (less reactive).
• Highly polarised bonds (bonds between atoms with different electronegativity) are easier to break.
• When bond length increases, the energy of filled orbitals increases and the energy of unfilled orbitals decreases.
• Longer bonds are easier to break.

  ~As the bond length increases, the energy of the anti bonding orbital (LUMO) decreases, thus reducing the HOMO-LUMO gap and increasing the efficiency of orbitals overlap.
• Longer bonds are more nucleophilic. As the bond length increases, the energy of the bonding orbital (HOMO) increases, thus reducing the HOMO-LUMO gap and increasing the efficiency of orbitals overlap.
• Fluorine is most electronegative.
• ~Alkyl halides are organic molecules containing a halogen atom bonded to an sp3 hybridised carbon atom.

  ~Vinyl halides have a halogen atom (X) bonded to a C-C double bond.

  Aryl halides have a halogen atom bonded to a benzene ring.

  ~Carbon sp2 hybridised.

  ~These are unreactive.
• ~Allylic halides have X bonded to the carbon atom adjacent to a C-C double bond.

  ~Benzylic halides have X bonded to the carbon atom adjacent to a benzene ring.

  ~sp3 hybridised

  ~Do participate in reactions.
• Nucleophiles are Lewis bases (electron donor) that can be negatively charged or neutral.
• When a neutral nucleophile is used, the substitution product bears a positive charge.