AoS2 - Organic Compounds, Naming, Structures and Physical Properties Flashcards
Organic Chemistry
Study of the compounds of carbon (with some exclusion)
Organic Compounds
- organic molecular compounds
- comprise over 90% of all known chemicals
- occur naturally and can be produced in the laboratory.
Hydrocarbons
- simplest class of organic compounds
- consist of hydrogen and carbon in chains of varying length
Types of Hydrocarbons
Aliphatic and Cyclic
Aliphatic Hydrocarbons
Carbon and hydrogen atoms are arranged in straight chains or branched chains.
Cyclic Hydrocarbons
Carbon atoms arranged in a ring structure.
Saturated Hydrocarbons
Contains only single carbon to carbon bonds
Unsaturated Hydrocarbons
Contains double or triple carbon to carbon bonds.
Families/Series of Aliphatic Hydrocarbons
Alkanes, Alkynes and Alkenes.
Use of Hydrocarbons
- fuels
- solvents
- lubricants
- raw materials for products such as plastics, fibres and explosives.
Homologous Series
Series of Hydrocarbons that have a similar chemical structure and similar chemical properties
Each compound in each series differs from the previous one by a CH2 group.
Alkane
CnH2n+2
Single Carbon to Carbon bonds only
Saturated
Alkene
CnH2n
One double Carbon to Carbon bond
Unsaturated
Alkyne
CnH2n-2
I triple Carbon to Carbon bond.
Unsaturated
Molecular Formula
Chemical formula that shows the total number and types of atoms in a molecule but not their structural arrangement.
Structural Formula
Graphic representation of the molecular structure, showing how the atoms are arranged.
Shows all covalent bonds.
Condensed Formula
Compact way of drawing the structural formula of a molecule. Covalent bonds are not shown.
Skeletal Formula
- Representation of the molecular structure in which covalent bonds are shown as line, but the atoms are not shown.
Other atoms are written in.
Structural Isomers
Compounds having the same molecular formula but different structures.
- Have similar chemical properties but can differ in some physical properties.
Straight Chain
C atoms bonded in a continuous chain.
Branched Chain
C atoms form a branch
What happens to the isomers as the molecules become larger?
They are able to form a greater number of isomers.
Naming Hydrocarbons
Named according to international union of pure and applied chemistry.
I C
Meth
2 C
Eth
3 C
Prop
4 C
But
5 C
Pent
6 C
Hex
7 C
Hept
8 C
Oct
9 C
Non
10 C
Dec
Prefix
Indicates number of C atoms in longest chain
Suffix
Refers to hydrocarbon type
- ane
- ene
- yne
Naming Alkanes
- identify longest chain
- identify name of branch
- number carbon atoms in the longest chain so side groups are on atoms with smallest number
Alkyl Groups
An alkane molecule with one less H
Two or more alkyl groups on same/different carbons
use
- di
- tri
- tetra
Two or more branches on the same carbon
- identify number for EACH branch
- List in alphabetical order.
Naming Alkenes + Alkynes
- identify longest chain containing double/triple bond
- number C’s so double/triple bond has the smallest number
Functional Group
An atom (halogen) or groups of atoms (other than hydrogen) that influence the chemical and physical properties of the compounds forming a homologous series.
Homologous Series of Functional Groups include
Haloalkanes
Alcohols
Carboxylic acids
Esters
Haloalkanes
Functional Group: Cl, Br, F
Prefix: chloro, bromo, fluoro
Dipole - dipole bonding
Alcohol
Functional Group (OH-)
- hydroxyl
suffix : “ol”
hydrogen bonding
Carboxylic Acid
Functional Group: COOH (carboxyl)
suffix = -oic acid
Hydrogen Bonding
Functional Groups (most important to least important)
- carboxylic acids
- alcohol
- alkyne = alkene
- alkane
- haloalkane
When naming, if more than one functional group is present
- the most important group determines ending
- all other groups form the prefix.
Bonding in Hydrocarbons
- non-polar molecules
- dispersion forces only
Bonding in Haloalkanes
- presence of halogen creates polar molecule
- dipole-dipole bonding
Bonding in Alcohol
- presence of Hydroxyl group creates polar molecule
- hydrogen bonding
Carboxylic Acid
- Presence of Carboxyl group creates polarity
- Two Hydrogen bonds.
Solubility
The ability of a substance to dissolve in a solvent
For an organic compound to be soluble
Intermolecular bonds of the substance and water must be broken
New bonds are formed between molecules.
Solubility in water
Must be able to break strong hydrogen bonds between water molecules.
Nonpolar molecules: weak dispersion forces hence insoluble.
Small Polar substances with hydrogen bonds are soluble.
Solubility with Hydrogen Bonds
- Solubility decreases as size of the molecule increases due to larger non-polar sections (hydrophobic section) that reduces impact of hydrogen bond
Chemical Property
Characteristic that becomes evident after a substance undergoes a chemical reaction/change.
Physical Property
Can be observed or measured without changing matter composition.
Melting + boiling points, viscosity, solubility
Viscosity
The resistance to flow as a liquid
Trends of Organic Compounds
- depend on intermolecular forces present
- strength dependent on: size of molecule, degree of branching and presence of functional groups.
Degree of Branching
Strength of forces decreases with increasing number of branches
Straight chain molecules are packed close, increasing strength
Branched chain cannot get close, decreasing strength.
Size of the molecule
Strength of forces increase with increasing size.
Presence of functional groups
- Strength increases with addition of dipole-dipole or hydrogen bonding.
Why are Carboxyl groups always on the end?
The carbon in the carboxyl group already bonded to three other atoms, it only has one bond available and is hence located on the end of the carbon chain.
General rule for smaller molecules
like dissolves like
polar – polar
What is percentage composition?
A relative measure of the mass of each different elements present in a compound.
Percentage composition formulas
Molar mass of element/molar mass of compound
Mass of the element/mass of the sample
Calculating mass of an element using percentage composition
- given mass and molecular formula
molar mass of element (including number)/ molar mass of compound x mass of compound.
What is the empirical formula?
Simplest whole number ratio of elements in a compound
Steps for calculating the empirical formula
- Determine the mass of each element
- Calculate the amount in mol
- Divide each element by the lowest mole quantity
- Express as a formula
Calculating number of mol of an element given mol of the whole compound
total mol x number of element atoms in compound
What is the molecular formula?
Actual number of each element in a compound
Steps for calculating molecular formula
- Determine empirical formula
- Determine molar mass
- Calculate by dividing molar mass required by molar mass of empirical formula.
Define Allotrope
Different physical form of the same element
What are allotropes of carbon?
- Diamond
- Graphite
- Fullerenes
Describe diamond
Covalent network lattice
- Each atom is covalently bonded to 4 other carbon atoms in 3 dimensions
- highest melting point
- hardest known substance
- chemically inert
- non-conductive
- insoluble in water
Provide examples of other network lattices
- Silicon
- Silicon Carbide
- Silicon dioxide
What carbon allotrope is this?
Diamond
Describe Graphite
- Covalent layer lattice
- Each carbon atom is covalently bonded to 3 other carbon atoms
- conductor of electricity, soft, weak and greasy
- high melting temperature
What intermolecular forces does graphite have?
Forces between layers are weak dispersion forces
Where is the fourth electron in graphite?
Fourth electron is delocalised and free to move between layers
What shape does Diamond have?
Tetrahedral
Why does Graphite conduct electricity while Diamond does not?
- Graphite has free moving delocalised electrons
- For electricity to be conducted, there must be free moving charged particles.
Why is diamond so hard?
- strongest form of intramolecular forces due to network lattice in which atoms are arranged
- Each carbon atom is covalently bonded to 4 other carbons
Practical uses for Diamond
Cutting tools and jewelry
Why does diamond have a high melting point compared to graphite?
- Diamond has carbon atoms arranged in a network lattice and has strong bonds in all three dimensions
- A network lattice is stronger than the intermolecular forces of graphite as more energy required to break these bonds
Why can graphite be used as a lubricants?
- Layer lattice structure
- Layers are held together by weak dispersion forces so they can readily slide past one another
- Has a very high melting point
Reactivity of hydrocarbons order
- Alkynes
- Alkenes
- Alkanes
The presence of a double or triple bond makes a hydrocarbon more reactive.
What are esters?
- a homologous series which contain an ester functional group
- creates a polar molecule which leads to dipole dipole bonding
What homologous series are esters made from?
Alcohols and carboxylic acids.
Naming esters
(alcohol)(acid-oate)
Why does boiling point increase with increasing chain length?
- number of dispersion forces increase
- results in stronger intermolecular forces which require more energy to break
Why are cyclic hydrocarbons insoluble in water?
- both substances have to be polar according to the like dissolves like rule
- hydrogen bonds are unable to be broken by the weak dispersion forces
Where are hydrocarbons found?
- crude oil
- processing oil produces useful substances
Why does the addition of a functional group change the properties?
- creates dipole or hydrogen bonding
- polar
- increases intermolecular force strength, melting and boiling points.
Why are carboxyl groups always on the end of the longest chain?
- Carbon is already bonded to 3 other atoms, it only has one bond available.
Properties affecting viscosity
- smaller molecules that have less atoms form less dispersion forces
- ## molecules require less energy to break bonds and can flow over one another easier
Largest source of crude oil
Fossil fuels
Crude oil is also known as
Petroleum that contains different length hydrocarbons
Distillation
separating two or more liquid components on the basis of boiling point differences
Fractional distillation
process used to refine (seperate) crude oil into its components
Hydrocarbons have different length chains so are seperated based on boiling points
Distillation in the laboratory
- process used to separate and purify liquids in the laboratory based on boiling points.
Substitution reaction
Atom in an alkane is replaced by a halogen in the presence of UV light and high temperatures
How many products are formed in a substitution reaction?
Two
Why is UV light required for a substitution reaction?
UV light provides the energy to break the covalent bond in the halogen molecule to produce two reactive halogen atoms each with an unpaired electron
Combustion reaction
- hydrocarbons are fuels that react with oxygen gas in a combustion reaction
complete combustion reaction
excess oxygen
incomplete combustion
limited oxygen (monoxide)
CO
Addition reactions
Alkene reacts with another substance to form a single product
- must be unsaturated
- often requires a catalyst
Bromine test
- bromine water has a characteristic orange colour
- loses this when combined with an unsaturated hydrocarbon
How are esters produced
Condensation reaction
Condensation reaction
- carboxylic acid and alcohol
- water is the product
- hydroxyl group must be on carbon 1
- acid required as a catalyst
Cracking/Decomposition
- process where large alkanes are broken down into smaller more useful hydrocarbons
Weak acids
- carboxylic acids
- in water, partially ionize to produce hydrogen ions
pH scale
- measures how acidic a substance is
Acidity
Measure of concentration of hydrogen ions
- the more hydrogen ions the more acidic
Alcohol pH
6
Carboxylic acid pH
3 - 4
Reactions of haloalkanes
made from alkanes using substitution or alkenes using addition
- starting material for synthesis
- creates polar bond
To produce a haloalkane
- react with hydroxide ions in a substitution reaction to produce an alcohol
Hydrolysis
- addition of water
- presence of water and heat
catalyst
speeds up chemical reaction
