2.4 - Organic compounds

Question 1

What is a hydrocarbon?

Answer 1

A compound containing hydrogen and carbon only

Question 2

What is the functional group of an organic compound?

Answer 2

The atom/ group of atoms that gives that compound its characteristic properties

Question 3

What is an homologous series?

Answer 3

A series of compounds that have that have the same functional group (a family of compounds)

Question 4

What is a saturated compound?

Answer 4

Is one that contains no C=C bonds

Question 5

What is an un-saturated compound?

Answer 5

Is one that contains C=C bonds. You can fit more elements onto the carbon atoms

Question 6

To name a compound you have to know the homologous series to which it belongs. The homologous section series in this section are:

Alkanes
Alkenes
Halogenoalkanes
Alcohols
Carboxylic acids

What are these compounds and what are the functional groups present in them?

Answer 6

Alkanes - Saturated hydrocarbons (C-C)
Alkenes - Unsaturated hydrocarbons (C=C)
Halogenoalkanes - Compounds in which one or more hydrogens in an alkane have been replaced by a halogen (Group 7, fluorine (F), chlorine (Cl), bromine (Br), iodine (I), astatine (At), and tennessine (Ts) )
Alcohols - (-OH)
Carboxylic acids - (-COOH)

Question 7

What do these compounds have as a suffix (and prefix) of? Give examples

Alkanes
Alkenes
Halogenoalkanes
Alcohols
Carboxylic acids

Answer 7

-ane (Methane)
-ene (Ethene)
prefix pf the halogen, suffix of -ane (Chloroethane)
-ol (Methanol)
-oic acid (Ethanoic acid)

Question 8

The name of a organic compound depends on the number of carbon atoms in the molecule. What are the stems that represent the number of atoms…
1
2
3
4
5
6
7
8
9
10
(count the longest continuous chain, it’s often drawn bent/ going round corners)

Answer 8

1 - meth
2 - eth
3 - prop
4 - but
5 - pent
6 - hex
7 - hept
8 - oct
9 - non
10 - dec

Question 9

Compounds names have the format of prefix- stem-suffix. What are the rules for naming organic compounds?

Answer 9

1) Find the longest carbon chain. This is the stem
2) Number the C atoms in the longest chain, starting from the end closest to any side chains or functional groups
3) Identify all the side chains and substituted functional groups using the appropriate prefixes, e.g. methyl (CH3) or ethyl (C2H3). If there is more than one side chain or substituted group the same, use di for 2, tri for 3 and tetra for 4
4) When writing full name, list prefixes in alphabetical order

Question 10

Give the names of these common functional groups:

NH2
F
Cl
Br
I
NO2

Answer 10

amino
fluoro
chloro
bromo
iodo
nitro

Question 11

What is a molecular formula?

Answer 11

The true number of atoms of each element in a compound

See NC 1

Question 12

What is the displayed formula?

Answer 12

Shows all the bonds and atoms in the molecule

See NC 1

Question 13

What is the shortened formula?

Answer 13

Shows the way the atoms are bonded but doesn’t include the bonds

See NC 1

Question 14

What is the skeletal formula?

Answer 14

Shows only the bonds between any carbon atoms in the molecule and any functional groups that may be attached. You won’t see the carbon and hydrogen atoms (unless the hydrogen atoms are part of a functional group)

See NC 1

Question 15

Each organic compound belongs to a particular homologous series. An homologous series is a set of compounds that:

All members follow a ______formula
Differ from their neighbour in series by ___
Have same ________ _______ and so very similar chemical properties
Have ______ properties that vary as Mr (length of chain) varies

Answer 15

general
CH2
functional groups
physical

Question 16

A polar molecule will have ________ dipole interactions which will increase _______ temp. The stronger the permanent dipole attractions and more ________ bonding there is, the more ______ an organic compound will be in water, as attractions will form with polar molecules.

Answer 16

permanent
boiling
hydrogen
soluble

Question 17

What are the general formulas of these organic compounds:

Alcohols
Aldehydes
Alkanes
Alkenes
Carboxylic acid

Answer 17

C(n)H(2n+1)OH
C(n)H(2n+1)CHO
C(n)H(2n+2)
C(n)H(2n+1)COOH
C(n)H(2n)

Question 18

What is the empirical formula?

Answer 18

Formula of a compound with the atoms of the elements in there simplest integer ratio

Question 19

The empirical formula could be the molecular formula but the molecular formula could also be a multiple of the empirical formula. The molecular formula of ethane = C2H6
Ratio of C:H in molecular formula is 2:6
Simplest ratio C:H = 1:3
Empirical formula of ethane =

Answer 19

CH3

Question 20

For organic substances, most experimental methods are based on burning a known mass of the compound in excess oxygen and measuring the masses of ____ and _____ ______ produced

Answer 20

water
carbon dioxide

Question 21

We can represent the combustion of a hydrocarbon in excess oxygen by the following equation:

CxHy + excess O2 —> x CO2 + Y/2 H20

If you know the masses of CO2 and H20 produced, you can calc the number of moles, x and y, hence finding the empirical formula of the hydrocarbon

moles = mass / mr

x = mass CO2 / 44
y = (mass H20 / 18.02) x 2

Divide this through by the smallest number to convert x and y into integer values

Answer 21

See NC 2

Question 21

What are structural isomers?

Answer 21

Compounds with the same molecular formula but different structural formulae (arrangement of atoms)

Question 22

What is chain isomerism?

Answer 22

This occurs when the carbon chain within the molecules is arranged differently (usually one has a straight chain and the others have branched chains)

See NC 3

Question 23

What is position isomerism?

Answer 23

This occurs when the functional group is in a different position in the molecule

See NC 3

Question 23

What is functional group isomerism?

Answer 23

Compounds with the same molecular formula but different functional groups

Question 24

In a ____ , the particles are held together rigidly and they can only vibrate about a fixed position. When the solid melts, the forces that hold it rigidly have to be overcome. Although there is less order in a liquid and the particles are further apart, significant attractive forces are still present and these have to be overcome when the liquid changes into a gas. This means that energy is needed to overcome forces whenever a substance melts or boils. This energy is generally in the form of ____. When comparing substances, the one that has a higher melting or boiling temp can be predicted by looking at the strength of these forces.

Answer 24

solid
heat

Question 25

In hydrocarbons, since the electronegativities of H and C are similar, hydrocarbons are non -polar. This means that only ________ ______ - _______ ____ Van der Waals forces are present between the molecules. These are weak ___molecular forces

Answer 25

temporary dipole - temporary dipole
Inter

Question 26

Intermolecular temporary dipole - temporary dipole forces act between the surfaces of the molecules. The more surface there is in contact the stronger the forces. This means that more energy is needed to over come the forces and the melting and boiling temps are higher.

Longer the _________ the more points of ______ (greater S.A), stronger _________ forces and hence more _____ needed to overcome them

Answer 26

hydrocarbon
contact
intermolecular
energy

Question 27

Why are the boiling/ melting temps of hydrocarbons effected by the shape of the molecule?

Answer 27

Different structural isomers will have different boiling temps because they have different surface areas that can be in contact.

See NC 4

Question 28

Why would functional groups effect the boiling temp of molecules?

Answer 28

Strongest intermolecular forces are hydrogen bonds, therefore those that form H bonds have a higher BP than those of similar size that cannot H bond

See NC 4

Question 29

What is Hydrogen bonding?

Answer 29

A special type of dipole-dipole attraction between molecules, not a covalent bond to a hydrogen atom. It results from the attractive force between a hydrogen atom covalently bonded to a very electronegative atom such as a N, O, or F atom and another very electronegative atom.

Question 30

The most significant intermolecular forces between water molecules are H bonds. Covalent compounds that can replace these bonds by forming new H bonds with water will dissolve.

Hence, can ____ dissolve in water?

Hydrocarbons
Alcohols
Carboxylic acids

Answer 30

Hydrocarbons (non-polar) cannot because they only form van der Waals interactions between molecules and are unable to form significant attractions with the polar water molecules

Alcohols and carboxylic acids can as they have -OH groups that can form H bonds with water