CEN2001 Organic Chemistry
Introduction to Organic Chemistry : Structure
and Bonding
What is organic chemistry?
- Carbon containing compounds were once considered available only
from living organisms (organ compounds) = Theory of Vitalism
- The synthesis of the organic compound urea in 1828 showed that
organic compounds can be prepared in the laboratory from non-
living material.
Organic chemistry (Carbon chemistry) mainly consists of Carbon (C) and
Hydrogen (H), but also much more elements out of the periodic table!
- Carbon in unique (4 covalent bonds & bonding with itself) due to
its central position in the second row of the periodic table
- Other elements of interest in organic chemistry : remaining
elements in the second row (Li, Be, B, C, N, O, F) as well as H, Si, P,
S, Cl, Br, I and many others.
What about electrons? Organic chemistry is often viewed as the study of
the movement of electrons between molecules. We write atoms, but often
we look at the electrons for information.
What is a molecule? An electrically neutral group of two or more atoms
held together by chemical bonds.
- Covalent bonding is most prevalent for organic chemistry! It is
based on sharing of valence electrons between two atoms.
- Atoms gain, lose and share electrons to fill their valence shell with
8 electrons (octet rule), and therefore we can make molecules.
An atom consists of negatively charged electrons, positively charged
protons, and neutral neutrons!
- Electrons form chemical bonds
- Atomic number = number of protons in its nucleus
- Mass number = sum of the protons and neutrons in an atoms
- Isotopes have the same atomic number but different mass
numbers.
, - atomic weight = the average weighted mass of its atoms
- molecular weight = the sum of the atomic weights of all the atoms
in the molecule
wave functions or orbitals tell us the energy of the electron and the
volume of space around the nucleus where an electron is most likely to be
found. The atomic orbital closer to the nucleus has the lowest energy.
Degenerate orbitals have the same energy.
How to draw molecules?
Lewis Theory = Draw Lewis structures via 7 step-plan!
1. Number of valence electrons
2. Skeleton
3. Single bonds in between atoms
4. Divide valence electron over outer atoms
5. Divide valence electrons over central atoms
6. Check octet rule
7. Make double, triple bonds if necessary
Neutral
Cationic (carbocation)
Anionic (carbanion)
Electronegativity is a measure of the tendency of an
atom to attract a bonding pair of electrons.
, - Higher electronegativity -> pulls electrons towards itself!
VSEPR Theory (Valence Shell Electron Pair Repulsion) = important
technique to predict bond angles and shapes of molecules. Electrons will
repulse each other and want to be as far away as possible
- Linear (180 degrees)
- Trigonal planar (120 degrees)
- Tetrahedral (109.5 degrees)
Drawing organic molecules
Zig-zags
4 rules to draw a good chemical structure
1. Draw chains and rings of atoms as zig-zags
2. Do not draw hydrogens attached to these carbons atoms!
3. Miss out the capital C representing carbon atoms
4. Draw other atoms (O, N, S) and functional groups
Nomenclature
Methyl, ethyl, propyl, butyl, pentyl etc.
‘’Cyclo’’ is used to indicate a ring!
General naming order for simple compounds =
PREFIX – PARENT – SUFFIX
- PREFIX gives position and sometimes
nature of substituents
- PARENT gives longest carbon chain
Introduction to Organic Chemistry : Structure
and Bonding
What is organic chemistry?
- Carbon containing compounds were once considered available only
from living organisms (organ compounds) = Theory of Vitalism
- The synthesis of the organic compound urea in 1828 showed that
organic compounds can be prepared in the laboratory from non-
living material.
Organic chemistry (Carbon chemistry) mainly consists of Carbon (C) and
Hydrogen (H), but also much more elements out of the periodic table!
- Carbon in unique (4 covalent bonds & bonding with itself) due to
its central position in the second row of the periodic table
- Other elements of interest in organic chemistry : remaining
elements in the second row (Li, Be, B, C, N, O, F) as well as H, Si, P,
S, Cl, Br, I and many others.
What about electrons? Organic chemistry is often viewed as the study of
the movement of electrons between molecules. We write atoms, but often
we look at the electrons for information.
What is a molecule? An electrically neutral group of two or more atoms
held together by chemical bonds.
- Covalent bonding is most prevalent for organic chemistry! It is
based on sharing of valence electrons between two atoms.
- Atoms gain, lose and share electrons to fill their valence shell with
8 electrons (octet rule), and therefore we can make molecules.
An atom consists of negatively charged electrons, positively charged
protons, and neutral neutrons!
- Electrons form chemical bonds
- Atomic number = number of protons in its nucleus
- Mass number = sum of the protons and neutrons in an atoms
- Isotopes have the same atomic number but different mass
numbers.
, - atomic weight = the average weighted mass of its atoms
- molecular weight = the sum of the atomic weights of all the atoms
in the molecule
wave functions or orbitals tell us the energy of the electron and the
volume of space around the nucleus where an electron is most likely to be
found. The atomic orbital closer to the nucleus has the lowest energy.
Degenerate orbitals have the same energy.
How to draw molecules?
Lewis Theory = Draw Lewis structures via 7 step-plan!
1. Number of valence electrons
2. Skeleton
3. Single bonds in between atoms
4. Divide valence electron over outer atoms
5. Divide valence electrons over central atoms
6. Check octet rule
7. Make double, triple bonds if necessary
Neutral
Cationic (carbocation)
Anionic (carbanion)
Electronegativity is a measure of the tendency of an
atom to attract a bonding pair of electrons.
, - Higher electronegativity -> pulls electrons towards itself!
VSEPR Theory (Valence Shell Electron Pair Repulsion) = important
technique to predict bond angles and shapes of molecules. Electrons will
repulse each other and want to be as far away as possible
- Linear (180 degrees)
- Trigonal planar (120 degrees)
- Tetrahedral (109.5 degrees)
Drawing organic molecules
Zig-zags
4 rules to draw a good chemical structure
1. Draw chains and rings of atoms as zig-zags
2. Do not draw hydrogens attached to these carbons atoms!
3. Miss out the capital C representing carbon atoms
4. Draw other atoms (O, N, S) and functional groups
Nomenclature
Methyl, ethyl, propyl, butyl, pentyl etc.
‘’Cyclo’’ is used to indicate a ring!
General naming order for simple compounds =
PREFIX – PARENT – SUFFIX
- PREFIX gives position and sometimes
nature of substituents
- PARENT gives longest carbon chain
