NUCLEOPHILIC SUBSTITUTION Flashcards
HALOGENOALKANES
What are the bond polarities of the halogenoalkanes? (2)
halogenoalkanes have a C-X bond, the bond is polar because halogens are more electronegative than carbon. going down the group the atom gets less electronegative.
what are the trends in solubility in the halogenoalkanes? (3)
the polar C-X bonds are not polar enough to make them soluble in water.
the main intermolecular forces are dipole-dipole and van der waals
halogen alkanes mix with hydrocarbons so can be used in dry cleaning.
what are the trends in boiling point in the halogenoalkanes? (3)
-boiling point increases with increased chain length
-boiling point increases going down the halogen group
-which is caused by increase in van der waals forces.
what are the most electronegative halogenoalkanes? (4)
-fluorine -most
-chlorine
-bromine
-iodine -least
what are the prefixes for each of the halogenoalkanes? (4)
-fluoro
-chloro
-bromo
-iodo
what is a primary amine? (1)
a primary amine has one alkyl group on the nitrogen atom.
what is a tertiary amine? (1)
a tertiary amine has three alkyl groups on the nitrogen atom.
what is a secondary amine? (1)
a secondary amine has two alkyl groups on the nitrogen atom.
what is the formula for a carboxylic atom? (1)
COOH
What is the formula for an alcohol? (1)
RCH2OH
what can halogenoalkanes be converted to? (3)
-alcohols
-amines
-nitriles
what are the other functional groups of alcohols? (2)
-carboxylic acid
-aldehyde
what are the other functional groups of primary amines? (2)
-secondary amines
-tertiary amines
what are the other functional groups of nitriles? (2)
-carboxylic acid
-primary amine
why are nucleophilic substitutions useful? (1)
they introduce new functional groups into organic compounds.
what is the nucleophile when halogenoalkanes react with cyanide ions? (1)
the cyanide ion.
what is the nucleophile when halogenoalkanes react with ammonia? (1)
the ammonium
what do curly arrows represent? (1)
are used to show how electron pairs move in organic reactions.
what is the leaving group? (1)
when the electron pair in the C-X bond moves to the halogen atom, X, making it a halide ion (the leaving group)
what are produced from the mechanism with halogenoalkanes and cyanide ions? (1)
nitriles are formed.
what is the overall reaction for halogenoalkanes with aqueous sodium (or potassium) hydroxide? (2)
R-X + OH(-) -> ROH + X(-)
Alcohol is formed
what is the nucleophile for halogenoalkanes with aqueous sodium (or potassium) hydroxide? (1)
the nucleophile is the hydroxide ion (OH-)
what is a nucleophile? (1)
reagents that attack and form bonds with positively or partially positively charged carbon atoms.
what is classified as a nucleophile? (1)
a nucleophile is either a negatively charged ion or has an atom with a partial negative charge.
what does the rate of substitution depend on? (1)
depends on the halogen; going down the group bond strength increases.
what are nucleophile substitution reactions? (1)
nucleophiles that replace the halogen in a halogenoalkane.
what are the most common nucleophiles? (3)
-the hydroxide ion (OH)
-ammonia (NH3)
-the cyanide ion (CN-)
what are the physical properties of the halogenoalkanes? (3)
solubility
-boiling point
-melting point
how reactive are the halogenoalkanes? (2)
how reactive the halogenoalkanes are depends on how reactive the C-X bond is, they are effected by two factors;
-the C-X bond polarity
-the C-X bond enthalpy
what are some properties of nucleophiles? (2)
-a nucleophile has a lone (unshared) pair of electrons which it can use to form a covalent bond.
-the lone pair is situated on an electronegative atom
how does bond polarity effect the reactivity of the halogenoalkanes? (2)
the carbon bonded to the halogen has a partial positive charge - its electron deficient - this mean that it can be attacked by reagents that are electron rich (nucleophiles). the C-F bond is most polar so is the most reactive.
how does the bond enthalpy effect the reactivity of the halogenoalkanes? (2)
the bond gets weaker going down the group. C-F is the stronger bond as it is a smaller atom, going down the group atoms get bigger minimising the attraction between the protons in the nucleus and the electrons in the outer electron shells.
what is a reaction mechanism? (1)
describe a route from reactants to products via a series of theoretical steps which may involve short lived intermediates.
