Halogenoalkanes Flashcards
Y12 (strand 1)
what is a halogenoalkane
compounds that contain an alkane chain or ring where a halogen atom or atoms is substitutes for one or more of the hydrogen atoms
how are halogenoalkanes divided into primary, secondary, and tertiary compounds
depending on what other atoms are bonded to the carbon atom to which the halogen is attached
what is the number of alkyl (r) groups of each carbon atom on primary, secondary, and tertiary halogenoalkanes
primary - 1
secondary - 2
tertiary - 3
how many h atoms attached to the carbon atom on which the halogen is bonded to on primary, secondary, and tertiary compounds
primary - 2
secondary - 1
tertiary - 0
what are the 2 types of reactions do halogenoalkanes undergo in different conditions
- nucleophilic substitution
- elimination
what is a nucleophile
an electron pair donor that are e- rich species that are attracted to delta + regions
name some common nucleophiles
OH-
CN-
H2O
NH3
why does polarity exist in some nucleophiles
due to differences in electronegativity meaning that the electron pair is shared unequally creating a permanent dipole
define nucleophilic substitution
a reaction where a nucleophile replaces a H on a molecule, forming a new bond with the carbon atom
what are the conditions for haloalkanes to react with NaOH or KOH
haloalkane must be warmed in an aqueous soln . of either NaOH or KOH
what is the general word equation for the reaction of halogenoalkanes with OH- ions
haloalkane + OH- -> alcohol + halide ion
what are the conditions for haloalkanes to react with sodium cyanide or potassium cyanide
NaCN / KCN has to be dissolved in ethanol and heated in reflux
what is the general word equation for the reaction of haloalkanes with CN-ions
haloalkane + CN- -> nitrile + halide ion + halide ion (lone pair)
what is the significance of the nucleophilic substitution reaction between haloalkanes and CN- ions in organic synthesis
- it increases C chain length
- the CN- group can then be converted into a carboxylic acid
what is the word equation for the reaction that forms carboxylic acid from nitriles
nitriles + HCl + H2O -> carboxylic acid + ammonium chloride
what is a hydrolysis reaction
where a bond is broken by reacting with a water molecule
despite not carrying a negative charge, why can NH3 act as a nucleophile
lone pair on the N is attracted to the slight positive on the C and can form a C-N bond
what is the general word equation for the reaction of haloalkanes with ammonia (excess)
haloalkane + ammonia -> amine + ammonium halide
what are the conditions required for nucleophilic substitution with ammonia
- excess ammonia
- reaction needs to be heated inside a sealed copper tube
how can the reactivity of different haloalkanes be compared
reacting them with water and silver nitrate
(although for testing purposes NaOH can be used to speed up the release of the halide ion)
how can the reaction of haloalkanes with alcohol be monitored using silver nitrate soln. (acidified with nitric acid)
- put the same vol. of each haloalkane in a test tube
- add the same volume and conc. of AgNO3 sol. to each
- time how long it takes for each one to precipitate over a piece of paper with an X on it
- can add ethanol to help to dissolve haloalkane
what would you see when you add silver nitrate to:
chloro-alkanes
bromo-alkanes
iodo-alkanes
chloro - white ppt
bromo - cream ppt
iodo - yellow ppt
what can you do if you are in any doubt about the product in the reaction of halogens to nucleophiles after adding silver nitrate
add NH3 - both conc. and dilute
chloro - dissolve in both
bromo - only dissolve in conc,
iodo - won’t dissolve
in reactivity, what is more influential - electronegativity or bond strength
bond strength
