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2015-10-24 08:06:16
Definitions for chemistry II
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  1. Differentiate between a chiral molecule and an achiral molecule
    • Chiral: a molecule whose mirror images are not superimposable.
    • Happens with molecules with one stereogenic centre (4 different substituents around a single carbon atom)
    • Achiral: mirror images are superimposable. Occurs when there is a plane of symmetry in the molecule
  2. What are enantiomers and diastereomers?
    • Enantiomer: stereoisomers that are mirror images of each other
    • Diastereomer: stereoisomers that are not mirror images of each other
  3. What is an optically active substance?
    A chiral substance that is able to rotate plane polarised light through a characteristic angle
  4. Define the following terms:
    ∂-amino acid, dipeptide, isoelectric point
    • ∂-amino acid: a carboxylic acid with an amino group on the ∂ carbon
    • Dipeptide: two amino acids which have reacted to create one molecule  (condensation)
    • Isoelectric point: the pH value where almost all molecules are in the zwitterion form (net charge=0)
  5. Describe 4 levels of proteins
    • Primary: the sequence of amino acids 
    • secondary: ordered structures via a network of H bonds
    • Tertiary: the 3D structure of a complete protein, made via intermolecular forces and disulfide bridges
    • Quaternary: How multiple proteins fit together in larger multiunit proteins
  6. If the two pKa values for threonine are 2,63 and 10.43, determine the pI value at the isoelectric point.
    • pI= pKa1 + pKa2
    •               2
    • =(2.63+10.43)/2= 6.53
  7. How can you tell if a carbohydrate has a D or L configuration?
    If in the fischer projection, the centre has the hydroxyle group on the right it is D- sugar
  8. Describe a chemical test that will help distinguish sucrose and maltose.
    Benedict's reagent: a copper containing reagent which can distinguish between reducing sugars such as maltose, (colour change observed) and non reducing sugars (no colour change)
  9. What is a heterocyclic compound?
    A heterocyclic compound is a cyclic compound that has atoms of at least two different elements as members of its ring(s).
  10. 1. Name 3 components of a nucleotide
    2. What type of bond links nucleotide together?
    3. What type of bond links adjacent nucleic strands
    • 1. Nitrogenous base, Phosphate group, Ribose sugar
    • 2. Phosphoester bond
    • 3. Hydrogen bond
  11. Define the terms 'monomer' and 'polymer'
    • Monomer: A repeating unit, which may react with itself or other potential repeating units
    • Polymer: A long chain consisting of one or more monomers
  12. Define step growth and chain growth
    • Chain growth: monomers become part of the polymer one at a time
    • Step growth: growing chains may react with each other to form even longer chains
  13. for the transition metals, how does atomic size change from the 3d series to the 5d series?
    • Very little difference between 3d and 5d electron atomic size
    • 4f electrons shield 5d electrons
  14. Give a systematic name for:
    tetraammine aqua bromido cobalt(III) bromide
  15. Define ligand, bridging ligand, bidentate ligand
    • Ligand: ions or neutral molecules that bond to a central metal atom or ion
    • Bridging ligand: a ligand that connects two or more atoms, usually metal ions
    • Bidentate ligand: Lewis bases that donate two pairs ("bi") of electrons to a metal atom