Alkanes Flashcards
Define alkanes.
Compounds containing only C-C and C-H single bonds
What is the general molecular formula for alkanes?
CnH2n+2
What is the general formula for cycloalkanes?
CnH2n
What is each successive member of a homologous series called?
a homologue
What is the repeating unit for alkanes?
CH2
What is CH2 called?
Methylene group
How does each homologue in the alkane series differ from one another?
Each homologue has one more C atom than the preceding member
What is a methylene group?
CH2
Are alkanes and cycloalkanes saturated or unsaturated?
They are saturated
What does saturated mean?
They contain the maximum number of H per C and have no double or triple bonds
What is the definition of a homologous series (in terms of alkanes)?
(5)
Molecules that have the same general formula
Homologues differ by CH2
Contain the same functional group
Show gradation in physical properties as molar mass increases
Homologues can be prepared by similar methods
What are branched alkanes?
Alkane molecules that have more than three C atoms that can be arranged in more than one way
How many C atoms are needed in order for an alkane to be branched?
Three
Give an example of an alkane that has a branched form.
Butane
What is the branched form of butane?
Isobutane
Describe the structure of isobutane.
2, methylpropane
A methyl branch exists off the second carbon in the longest chain
In general when is ‘iso’ used in relation to branched alkanes?
When there is one methyl group attached to the longest carbon chain
In general when is ‘neo’ used in relation to branched alkanes?
When there is two methyl groups attached to the carbon chain
What is an unbranched alkane often called?
3
An n-alkane
A normal alkane
An unbranched alkane
How many structural isomers does pentane have?
Three
List the three structural isomers of pentane.
Pentane
Methylbutane / isopentane
Dimethylpropane / Neopentane
What is methylbutane more commonly called?
Isopentane
What is dimethylpropane more commonly called?
Neopentane
What is nomenclature?
The naming of organic compounds
Who regulates the naming of organic compounds?
IUPAC
What does IUPAC stand for?
The International Union for Pure and Applied Chemistry
What is the word equation for naming alkanes?
Prefix - Parent - Suffix
In naming alkanes, what is the prefix?
The name and position of substituents
E.g 2-methyl____
In naming alkanes, what is the parent?
The length of the longest carbon chain
E.g. ___prop___
In naming alkanes, what is the suffix?
The main functional group
E.g. ________ane
What is CH3 called?
a methyl group
What is C2H5 called?
An ethyl group
What is C3H7 called?
A propyl group
What is C4H9?
A butyl group
What is C5H11?
A pentyl/amyl group
What is a methyl group?
CH3
What is an ethyl group?
C2H5
What is a propyl group?
C3H7
What is a butyl group?
C4H9
What is a pentyl/amyl group?
C5H11
What does a squiggly line indicate in skeletal structures?
They indicate that the group is attached to a substituent of some kind
What prefix is used when naming cycloalkanes?
Cyclo before the alkane name
What is the smallest possible cycloalkane?
Cyclopropane
What is the smallest possible cycloalkyl?
Cyclcopropyl
What does the skeletal structure of cyclopropane look like?
A triangle
How are carbon atoms in a molecule classified?
Based on the number of C-C bonds that are present
What determines the reactivity of a carbon atoms?
The number of C neighbours that a C atom has
What four types of carbon atoms can be found in alkane structures?
Primary
Secondary
Tertiary
Quaternary
What is a quaternary carbon?
A carbon attached to four other carbons
What is a functional group?
A specific atom or group of atoms which determines an organic compound’s chemical reactivity and physical properties
Name a functional group?
Haloalkanes (alkyl halides)
What two groups are not considered functional groups but are often found in alkane structures?
Alkyl and cycloalkane
Why are alkyl and cycloalkane substituents not functional groups?
This is because they are looked upon as being just part of a molecule’s framework
What are haloalkanes?
Chemical compounds in which one or more of the H atoms in an alkane have been replaced by a halogen atom
List the halogens.
4
Fluorine
Chlorine
Bromine
Iodine
What are the halogens often abbreviated to?
X
Are haloalkanes saturated or unsaturated?
They are saturated
What is the general molecular formula for monosubstituted haloalkanes?
CnH2n+1X
What is CH3F?
Fluoromethane
How do you change the halogen substituent?
Change the ‘ine’ to ‘o’
Fluorine to fluoro
Which is named first an alkyl substituent or a halo-substitutent?
They are names based on alphabetisation
What letter is used to represent an alkyl group?
R
What are isomers?
Isomers are molecules with the same number and type of atoms but show different spatial arrangements
What are structural (or constitutional) isomers?
Compounds with the same molecular formula but different structural formulas
How many different types of structural isomerism are there?
Three
What are the three types of structural isomerism?
Chain isomerism
Position isomerism
Functional isomerism
What is chain isomerism?
Isomers that arise because of the possibility of branching in C chains
What is position isomerism?
Isomerism where the basic C skeleton remains unchanged but important groups are moved around on that skeleton
What is functional group isomerism?
Isomers contain different functional groups, that is, they belong to different families of compounds
What is petroleum?
A liquid mixture containing hundreds of substances
Describe the relationship between boiling point and unbranched and branched alkanes.
(2)
The boiling point of unbranched alkanes increase with the number of C atoms
The boiling point of branched alkanes are lower than those of their unbranched isomer
What three types of attractive forces?
Dipole/Dipole
Dipole/ induced-dipole
Induced-dipole/induced-dipole
What type of attractive force is present in alkanes?
Induced-dipole/ induced-dipole attractive force
