Basics of Organic Chemistry
Objective: I need to provide you with enough information
so that you can understand the basic chemical properties of wood
and wood products. There is alot of information out there on the
Web to help you with organic chemistry. My CHEM 2514 home page
may be useful, as would be Organic Online. If you are having problems
with this material, you need to get help as soon as possible.
Falling behind now will really mess up your performance in this
class.
Important Concepts
- Functional Groups. Organic molecules have preferred
ways of forming covalent bonds, and these are called functional
groups. With respect to wood chemistry, the more important functional
groups are those of carbon, hydrogen and oxygen. The functional
group handout at the end of this page has most of the common
ones. The ones we need to know for wood chemistry are those involving
carbon, hydrogen and oxygen. Nitrogen and halide-containing functional
groups are not as important. Click
here for downloading more examples of identifying functional
groups.
- Covalent, hydrogen and ionic bonding.
- Polarity. Elements in the periodic table have charges
depending on whether they want to get electrons or give them
up to complete their outer shell. Atoms towards the right side
of the table like to get electrons and are considered electronegative.
Atoms that would rather give electrons up (to fill the outer
shell at the next lowest level) are electropositive. The electronegativity
of a few elements are shown below:
- Acids and Bases. Acids donate hydrogen ions and bases
accept them. If an acid donates its proton it becomes a conjugate
base. Thus it stands to reason that if a base picks up a hydrogen
ion it becomes a conjugate acid. When we deal with acids at bases
in wood chemistry, we will invariably be discussing it in aqueous
systems. The measure of acid/base strength in aqueous systems
is via pH: pH =1 is acidic and pH 14 is alkaline (basic). pH
is a log scale so decreasing the pH by one unit increases the
hydrogen ion concentration 10 fold.
- Major Chemical Reactions. Oxidation, reduction, hydrolysis
and condensation.
ORGANIC CHEMISTRY TERMS WHICH RELATE TO WOOD CHEMISTRY
- Chirality---a chiral object is one that cannot be
superimposed on its mirror image. Real-life examples include
your hands, shoes, and gloves. There is a lack of symmetry.
The word is Latin for handedness. A chiral center within a molecule
is one where 4 different groups are attached. An achiral molecule
has a plane of symmetry and are therefore superimposable (a coffee
mug is a real-life example of this.
-
- Covalent Bonding---a sharing of electrons by two atoms.
Most organic compounds have this type of bonding pattern. Carbon
pretty much always has covalent bonds. A fair bit if energy is
usually require to break a covalent bond.
-
- Hydrogen Bonding---an "attraction" more
than a true chemical bond, and occurs with a hydrogen atom bonded
to an oxygen or nitrogen. Oxygen and nitrogen have unshared electrons
and thus a slightly negative charge. A partially positive hydrogen
of one molecule is attracted to the unshared pair of electrons
of another molecule. This type of attraction is due to the uneven
distribution of charges and is termed a dipole. Hydrogen
bonding results in proteins taking their three-dimensional shape,
DNA taking on the double helix, and cellulose being crystalline.
-
- Ionic Bonding---is the result of a transfer of electrons
from one atom to another. Salts such as sodium chloride (NaCl)
are a classic example of this. In aqueous solution, ionic bonds
are associations and not firm attachments like a covalent bond.
-
- Isomerism---geometric-results from rigidity
in molecules and occurs in two classes of compounds: alkenes
and cyclic compounds. stereoisomers-same structure but
different arrangement in space. Enantiomers-a pair of
molecules that are non-superimposable mirror images. A single
enantiomer is optically active, it rotates plane polarized
light.
-
- Polarity-is related to the "type" of covalent
bond formed and the establishment of a dipole. Carbon-carbon
and carbon-hydrogen bonds are considered non-polar, that is the
two atoms share the pair of electrons equally. Compounds like
H2O, CH3OH (methanol) or CH3CH2OH (ethanol) for example, contain
non-polar bonds. The oxygen has a greater attraction for the
shared electrons which causes an uneven distribution of electron
density. Thus the high polarity of water leads to hydrogen bonding.
- Functional
Group Handout.
- Principles
of Covalent and Hydrogen Bonding
- Back to the
Wood 3434 Information Page