Organic Chemistry Module 5

1
Organic ChemistryModule 5
Prof Steve Glover Riggs Building
2
Topic 5AIntroduction
3
Carbon
SOOT
DIAMOND
GRAPHITE
BUCKY BALLS
4
Carbon the basis of life
C
C Nitrogen
C Nitrogen Oxygen
C Nitrogen Oxygen Phosphorous
DNA
5
Organic chemistry
2

• Organic chemistry is the chemistry of CARBON
  containing compounds
• Berzelius 1808 "Organic" substances as they
  were known could not be synthesised in the
  laboratory from "inorganic" materials, because it
  was believed that a "vital force" which was
  possessed only by living organisms was necessary
  to produce organic compounds.

6
Organic chemistry
2

• August Kekulé 1830Organic chemistry is the
  chemistry of CARBON containing compounds.
• Leopold Gmelin 1848Organic chemistry is the
  chemistry of carbon containing compounds which
  occur naturally
• Not quite but fairly close to the truth.

7
Studying organic chemistry
2

• Learn the language of organic chemistry how to
  name and identify organic chemicals
• Be able to draw the structures of organic
  chemicals
• Learn the various categories of organic
  chemicals
• Learn what are their properties
• Learn what are their characteristic reactions
• Understand how and why organic chemicals react
  the way they do

8
Why is carbon special
3

• Carbon carbon and carbon hydrogen covalent
  bonds are extremely strong ( CC bond energy of
  350kJmol-1).
• Carbon can form single, double and triple bonds
  readily.
• Can form a huge variety of chains and rings (by
  joining ends of chains).

9
Covalent bonds
3

• Covalent bonds are formed by the sharing of a
  pair of electrons between two atoms with little
  or no differences in electronegativity (at least
  smaller than 1.9)
• Each atom attains a closed shell electronic
  configuration (satisfies the octet rule) for at
  least some of the time
• Covalent bonds are depicted by lines between
  bonded atoms, eg

10
Multiple bonds
3

• Carbon can form more than one covalent bond with
  a neighbour, in which case we draw several lines
  between the atom
• Triple bonds eg HCN

Double bonds eg ethylene
11
Carbon containingcompounds
3

• Over10 million compounds listed in Chemical
  Abstracts and most are organic.
• Chains and rings can be formed

12
Tetrahedral carbon
4

• We note that carbon is tetravalent in all cases,
  ie forms four bonds to other atoms.
• The carbons are not flat. The Lewis structures
  represent carbon at the centre of a tetrahedron,
  eg methane
• Bonding electron pairs repel one another least
  this way.

13
Lewis structures
4

• Carbon and hydrogen differ in electronegativity
  by 0.4
• Carbon forms strong covalent bonds with itself
  and with hydrogen

14
Lewis structures
4

• Covalent bonds can be represented by Lewis
  formulas which show outer shell (valence)
  electrons around the atoms.
• Often only those electron pairs involved in
  forming the covalent bond are shown as a
  shorthand device.
• We simplify this to line-bond formulas where a
  single line represents each shared electron pair
  e.g.

15
VSEPR
4

• Valence-shell electron repulsion explains the
  geometry of a wide range of molecules

180
120
120
16
Polarity in organics
5

• Carbon bonded to electronegative atoms results in
  polar
• bonds.

17
Models of organics
6

• Density surfaces and electrostatic potential
  surfaces

18
Resonance in carboxyl groups
6

• Lone pair on oxygen can delocalise onto the
  carbonyl oxygen

Use double-headed arrowsto show movement of
electrons
19
A chemists shorthand3-D representations
7
20
A chemists shorthandformulas ethane (C2H6)
7

• Empirical formula CH3
• Molecular formula C2H6
• Structural formula
• Condensed formula CH3CH3 or CH3 CH3

21
A chemists shorthandfor pentane (C5H12)
7

• Skeletal for CH3 CH2 CH2 CH2 CH3
• Hydrogens omitted. They are understood to be
  there to complete the valencies.