Halogenoalkanes and hydrolysis reactions Flashcards
define nucleophile
a species that donates a lone pair of electrons to form a covalent bond with an electron-deficient atom
what is a hydrolysis reaction?
a reaction in which water or hydroxide ions (OH-) replace an atom in a molecule with an OH group
what is the general formula of halogenoalkanes?
CnH2n+1X where X is a halogen atom. the equation can be simplified to RX where R is an alkyl group
can you have different numbers of halogen atoms in halogenoalkanes?
yes, and this is represented by a number preceding the X in the general formula, for example, 1,2 dichloropropane would be part of the series abiding by the general formula CnH2n+1X2
why are halogenoalkanes reactive?
because they have a halogen to carbon bond which is polar as the halogen has a higher electronegativity than carbon. The carbon atom joined to the halogen is always slightly positive, or electron-deficient, so this is what makes halogenoalkanes react as they do.
why are hydrocarbons less reactive than halogenoalkanes?
hydrocarbons contain hydrogen and carbon atoms only, which have similar electronegativities, their bonds are almost non-polar, while halogenoalkanes contain a halogen carbon bond where the halogen has a higher electronegativity than carbon, so the C-X bond is polar.
what is trend of electronegativity down group 7?
decreases from fluorine to iodine
what does ‘lysis’ mean?
refers to splitting, like splitting water in hydrolysis and splitting compounds in electrolysis
what is the abbreviated formula of CH3-CH2-CH2F ?
RX
what is the abbreviated formula of CH3-CHBr-CH3 ?
R2CHX
what does ‘nucleo’ mean?
positive charge
what does ‘phile’ mean?
liking
how many alkyl groups are in this compound, (CH3)2 CCl-CH2-CH3 ? and what classification is it? (primary, secondary etc…)
three and tertiary
what are nucleophiles attracted to?
slightly positive or electron deficient parts of molecules.
halogenoalkanes are
a homologous series of compounds with the general formula CnH2n+1 X
X represents
a halogen atom
R represents
an alkyl group
examples of alkyl groups are
methyl or ethyl
the simplified formula for halogenoalkanes is
RX
the simplified formula of halogenoalkanes is RX because
R represents any alkyl group and X represents the halogen atom present in the compound
alkyl groups are
alkanes missing one hydrogen
the number of halogen atoms in a halogenoalkane can be
more than one
the general formula for halogenoalkanes containing two halogen atoms is
Cn H2n X2
the general formula for halogenoalkanes containing three halogen atoms is
Cn H2n-1 X3
the most notorious halogenoalkanes are
chlorofluorocarbons (CFCs for short)
CFCs contain
both chlorine and fluorine
CFCs were used in
aerosol cans
CFCs can
damage the ozone layer in the atmosphere, so have been phased out
when naming halogenoalkanes with more than one type of halogen atom,
name the halogen prefixes in alphabetical order
the prefix numbers should
be as small as possible when added together, and their sum cannot exceed the length of the longest carbon chain used in the naming
a primary halogenoalkanes means
the carbon atom to which the halogen atom is bonded is itself bonded to only one other carbon atom
a secondary halogenoalkanes means
the carbon atom to which the halogen atom is bonded to is itself bonded to two other carbon atoms
a tertiary halogenoalkane means
the carbon atom to which the halogen atom is bonded to is itself bonded to three other carbon atoms
the halogenoalkanes CH3X is
primary
hydrocarbons contain
only hydrogen and carbon atoms, which have similar electronegativities, so their bonds are almost non-polar
hydrogen and carbon atoms have
similar electronegativities
bonds which contain atoms of similar electronegativities are
almost non-polar
halogen atoms have a higher
electronegativity than carbon
partial charge for polar bonds is shown by
δ+ and δ-
the polarity of the C-X bond ……….. as halogens from further down Group 7 are present
decreases, because the electronegativity of halogens decreases down Group 7
the carbon atom joined to the halogen is always
slightly positive, δ+ or electron deficient part of the molecule
halogens are reactive because of
the slightly positive carbon atom joined to the halogen
δ+ carbon atoms or electron deficient carbon atoms attract species called
nucleophiles
nucleophiles are either
negative ions or molecules with a slightly negative atom
nucleophiles always
use (donate) a pair of lone electrons when attacking
nucleophiles form……. when attacking
a covalent bond with an electron deficient atom
when a halogenoalkanes is added to water
a reaction begins
the reaction between a halogenoalkane and water
may take a period of time to complete
a water molecules contains
polar polar bonds
in a water molecule, the oxygen atom is and the hydrogen atoms are
δ- O and δ+ H
in a hydrolysis reaction with a halogenoalkanes, the δ- oxygen atom in the water is attracted to
δ- oxygen atom in the water is attracted to the δ+ carbon atom in the halogenoalkane
hydrolysis reaction with halogenoalkanes results in the production of
an alcohol
the equations for the hydrolysis reaction with a halogenoalkane are
RX + H2O = ROH + HX
or
RX + H2O = ROH + H+ + X-
the hydrolysis reaction with halogenoalkanes are difficult to observe as
both organic substances, halogenoalkane and alcohol, are colourless, so no colour change can be seen
in the hydrolysis reaction with a halogenoalkane,
the C-X bond breaks, so the RX molecule break into two parts, the R(alkyl group) and the X (halogen atom). The R group then combines with the OH group of water
