Chemistry Unit 4 SAC 1

Organic compounds essentially comprise of:

• a structure of carbon atoms

• Hetero atoms, occasionally forming part of the structure, but usually are for functional groups, and determine the properties

• Hydrogen atoms that complete the bonding, and occasionally play important roles as members of functional groups

• Relatively high bond strength and stability between C atoms and to a range of other atoms

Tetrahedral structure

4 single bonds

Trigonal planar

1 double + 2 single

Linear

1 single + 1 triple or 2 double

What do the wedge and dash mean when drawing the 3d structure?

Wedge points out of the page, dash points in to the page

When naming a molecule with more than one double bond, or triple bond, or functional groups, what prefix do you need to add and does it count in the alphabetical order?

Di- or tri- and no it doesn’t

Homologous series

Family of same functional group, with different numbers of carbons

What is a structural isomer

Molecules with the same chemical formula but with different bonding connections between the atoms

What is a conformation

When rotations occur around a single bond, leading to different appearances in structure, however, they are not isomers and the bonding is not different

What is the naming conventions of an alkane

1. Name the parent chain (longest continuous chain)

2. Substitute to are listed with the suffix -yl. With di and tri added if multiple are added

3. Substituent numbers are counted from the end of the parent structure that gives the lowest first substituent number

4. Substituents are listed alphabetically not numerically. “Di” etc don’t affect this

With alkenes and alkynes, what are the bonds numbered to give

The lowest possible number to the position of the multiple bond.

What is a saturated compound

Has the highest possible number of hydrogen atoms for the number of carbons. CnH2n+2.

What does the presence of multiple bonds do to effect saturation

It means there are fewer bonding sites, thus the compound is unsaturated. Each additional bond reduces the number of H atoms by two and corresponds to one degree of unsaturation

What is a cycloalkane and is it unsaturated.

A cycloalkane is a ring of carbon atoms, named as a derivative of the largest ring present. They may appear to be unsaturated due to the reduced number of H atoms, however, due to the fact that the most h atoms that could bond to a 6 carbon cyclo is 12, it must be saturated. As it doesn’t have multiple bonds

What is benzene, and what makes it aromatic?

Benzene is a special structure that is unsaturated, containing 6 C with 3 double bonds, this ring is completely symmetrical, and the fourth valence electron on each carbon atom is delocalised and effectively shaped with all other carbon atoms in the ring, this gives it additional stability, and this especially delocalisation of valence electrons is called aromaticity.

What is the Chloro- functional group

• increases the number of electrons, thus stronger DF

• Boiling point is higher than alkanes

• May be more polar than hydrocarbons, but not sufficiently polar to dissolve in water

• Essentially non polar, and good solvents of grease and oil

• Neutral (not acidic or basic)

The Hydroxy group -OH (-ol) or (hydroxy-)

• O-H bond allows for H bonds

• Boiling point is higher than Alkanes

• Polar, and can dissolve in water as long as hydrocarbon portion is not too large for the number of -OH present

• Neutral

The amino group -NH2, -amine or amino-

• N-H bond allows for H bonds

• Boiling point are higher than alkanes

• Moderately polar

• Small amines are able to dissolve in water

• Basic as they can accept H+ ions to form R-NH3+ (make the + obvious when drawing)

Carboxy group -COOH (-oic acid) or (carboxy-)

• O-H allows for H bonds

• Boiling point is much higher than alkanes

• Polar, can dissolve in water except if hydrocarbon portion is too large

• Must be at the end of the chain, therefore always C1

• Weak acids, can lose the H ion and from a carboxylate ion, which can take in a + ion to form a metal -oate

How is an ester formed

A carboxy group will react with a hydroxy group t o from a new linking functional group called an ester group. A small molecule is split out hence a condensation reaction

How does the reaction occur and what is the role

The reaction is performed by heating the carboxylic acid and the alcohol together in the presence of a catalyst such as conc Sulfuric acid, which has 2 roles

• catalyst

• Hydroscopic → absorbs H2O as it forms which increases yield

How is an ester named

1st name - name of the alcohol

2nd name -acid with -oate

Ie ethyl propanoate

Aldehydes

• suffix -al

• Double bond O and an H

• Only on the end of the chain

Ketone

• -one

• Middle of the chain, and is a double bond O

• Numbering required

(Primary) Amide

• double bond O and an -NH2 group

What are secondary and tertiary amides

They have additional substituents attached to the N atom

Dispersion forces

• stronger in molecules with more electrons

• Only type of intermolecular bonding in non polar molecules

• Unless they are very strong, or the only type of intermolecular bonding, the effect of dispersion forces are relatively weak

Dipole dipole

Occur when a molecule is a permanent dipole, resulting from having:

• Polar bonds arise from atoms with large electronegativity differences sharing electrons

• Some element of asymmetry such that the effects of all the polar bonds do not cancel

Hydrogen bonding

• 10x stronger than dipole dipole

Requires:

• one molecule with a H atom bonded directly to N, O, F

• A second molecule with a free non bonding electron pair on a N, O, F

ion dipole

Occurs between a polar molecule like water and a cation or anion

• the o atom (-) of a water molecule will be attracted to a cation

• The H atom (+) in a water molecule will be attracted to an anion

What happens to the properties of a homologous series when you add a methylene group

No effect except the the strength of the dispersion forces

Melting and boiling point

Governed by the strength of the intermolecular bonding and will tend to be higher for molecules that have:

• More electrons, therefore stronger dispersion forces

• More polar functional groups that can form dipole dipole or H bonds

Solubility in water

To dissolve in water, molecules must be able to form bonds to water that can compete with and overcome H bonds

• water solubility increases with the presence of functional groups (hydrophilic) that allow hydrogen bonding with water

• Water solubility decreases with larger non polar regions (hydrophobic) as they cannot bond with water

If a liquid can mix with water at a ratio, and there is no solubility limit, it is called

Miscible

Viscosity

Low viscosity = runny

• viscosity increases as the intermolecular bonding gets stronger, since the more strongly attracted molecules will have more difficulty moving past one another

• Highly temperature dependent as temperature increase, the intermolecular attractions have less effect and viscosity decreases.