CHM 412Introduction

Structures ofpure carbon(allotropes)

CHM412 deals with organic compounds of carbon. E.g. methane – the simplest organic carbon based structure). Representations:

http://butane.chem.uiuc.edu/pshapley/GenChem2/B2/1.html

Structural formulae, and skeletal representations of other carbon based structures(propane and 1-Hydroxy-3-methyl-but-3-en-2-one)

• Exact structure (geometry) around a particular C atoms is governed by its hybridizationhybridization.

Hybridization:Atomic orbitals on one atom mix together when

reacting with another atom to produce new hybrid orbitals, which have

a) New shapesb)New energiesc) New angles

• General formula sp(n-1)

where n=number of σ bonds.

http://w

ww

.sparknotes.com/chem

istry/organic1/orbitals/section1.rhtml

sp3

sp2

sp

2 π bonds

Carbon structures – localized AT the carbon.

sp3 hybridization (4 σ bonds)

• As molecules form, hybridization occurs because the resulting molecule is more stable. Better overlap = stronger bonds = more energy given out when formed = more stable (ENTROPY INCREASES)

etc...

http://chemistry.umeche.maine.edu/CHY251/Hybrid.html

1.2 The nature of chemical bonding: Covalent bonding

Covalent bond when pair of e- is shared shared between two atomsbetween two atoms, each e- coming from one each e- coming from one of the atomsof the atoms.

A Dative covalent bond is where the shared pair of electrons came from just one atom.

It is the mutual attraction for one atoms outer e- buy another atom that is responsible for bonding.

Electronegativity

http://chemistry.stackexchange.com/questions/4087/oxidation-number-of-nitrogen-in-kcnhttp://www.youtube.com/watch?v=93G_FqpGFGY

1.3 Polar molecules:

• A dipole is a region of uneven charge distribution. A bond dipole has to do with the distribution of charge in a bond.

• A molecule is non-polar if the sum of the bond dipoles is zero, and is polar if the sum of the bond dipoles is non-zero (i.e. the bond dipoles do not cancel).

1.3 Polar molecules:

• X-X type bonds have even electron distn as each atom has the same attraction (affinity) for the electrons in the covalent bond.

• X-Y bonds have dipoles, the electron density being more towards the most electronegative atom. You need to consider the shape (which is a function of the bonding it has) to see if the bond dipoles cancel. CO2 has polar bonds but is not a polar molecule. AlCl3 has polar bonds but is non-polar. O2 non-polar molecule, H2O polar. NH3 is polar.

1.4 Intermolecular forces (IMF’s)

• Three types for a pure substance:• Hydrogen bonds (strongest)• Dipole-dipole interactions• London dispersion forces.

1.4 Intermolecular forces (IMF’s)• These are attractions between independent units eg. Two

water molecules, or an ammonia molecule and an Na+ ion, or an I2 molecule with another I2 molecule. DO NOT fall into DO NOT fall into the common misconception that they are covalent bonds. the common misconception that they are covalent bonds. They are not. They are not. IMF’s are responsible for a substances boiling point (and significantly to their mpt) and other effects such as ability to solvate (‘dissolve’) other molecules. When it comes to solubility you can follow the general rule: Like dissolves like. I.e. polar substances dissolve polar substances, and non-polar substances dissolve non-polar substances. Substances that don’t have H-bonding themselves e.g. ethanal, can engage in H-bonding with solvents that do can exhibit H-bonding e.g. water

1.3 Polar molecules:

Video: Major Intermolecular Forces with Dr Paul McCord http://www.youtube.com/watch?v=S8QsLUO_tgQ

1.4 Intermolecular forces (IMF’s)

Video: Polar bond - uploaded by Tuan Danghttp://www.youtube.com/watch?v=LKAjTE7B2x0

See also: Intermolecular forces - uploaded by Adam Lundquisthttp://www.youtube.com/watch?v=1TzTnDmpOP8and Intermolecular Attractions - Induced dipole, Dipole, Hydrogen Bonding, Ion http://www.youtube.com/watch?v=dQ33TVQCfyY

1.6 Functional groups

• A function group is an atom or sequence of atomsatom or sequence of atoms that alter the electron densityalter the electron density of a saturated hydrocarbonof a saturated hydrocarbon.

• They induce/introduce polarity into the hydrocarbon and alter bond strength.

• Saturated hydrocarbons are very low in polarity, so are do not interact (ie are not ‘attacked’ i.e. are unreactive towards polar compounds), and have strong bonds so not very easy to break up the hydrocarbon.

http://blog.tutorvista.com/2011/12/functional-group/#

• Nalorphine. A drug that acts to reverse the effects of morphine and other narcotics.

http://blogs.educationscotland.gov.uk/nqscience/2010/12/22/new-higher-chemistry-resource-functional-groups-in-complex-molecules-and-their-effect-on-physical-properties/

CC

C

O

C

H

O

ketonesaldehydes

"carbonyls"

&

C

O

O

H

C

X

O

catboxylic acids carboxylicderivatives&

OHOH OH

OH

alcohols (1o, 2o, 3o)

&

Aliphatic alcohols

phenol

An aromaticalcohol

alkanes alkenes

Benzene (an 'aromatic')NH2

N

H

N

amines (1o, 2o, 3o)

CHM 412 Functional groups

1.7 Empirical, molecular and structural formula

• Empirical formula = simplest whole number ratio of atoms in a compound.

•Molecular formula = Actual ratio of atoms in a particular molecule. Benzene, C6H6 = molecular formula, but empirical formula = CH.

• Ethane = C2H6 molecular formula and empirical formula = CH3

• Note: ( Empirical formula ) x n = molecular formula, here n = 1,2,3,4 depending on the exact molecule. Useful when presented with data by mass.

• • e.g. by mass: 56.5% K, 8.7% = C and 34.8%• Divide the %mass by the atomic MASS, K2CO3

1.8 Structural isomerism: chain, position & functional group

• Isomerism (Iso = one, mer = ‘thing’, so one particular thing) :There are various ways to rearrange the same atoms, each way is called an isomer.

• e.g. molecular formula C3H8O, C3H6O,.

1.9 Cis-trans isomerism

• This is one of the categories called stereo isomerism. The same sequence of atoms occurs but they differ in their position in 3D space.

• You need a bond of restricted rotation (usually a C=C, or a ring) AND two different atoms (or sequences of atoms on EACH C in the restricted bond)

• Cis – SIStersame family = same side

• Trans transatlantictranspacific

• = across

http://www.elmhurst.edu/~chm/vchembook/209cistrans.html

Geometric IsomerismWhat Do cis- and trans- Mean in

Chemistry?

• http://chemistry.about.com/od/organicchemistry/tp/Geometric-Isomerism.htm

1.10 Homolytic and heterogenic breaking of covalent bond

• Homolytic: The breaking of a covalent bond where one electron of the (breaking) bond goes onto each atom. (mind aid: The bond breaks evenly)

• Heterogenic. The breaking of a covalent bond where both electrons of the (breaking) bond goes onto only ONE of the atoms. (mind aid: The bond breaks unevenly)