13.2- NUCLEOPHILIC SUBSTITUTION IN HALOGENOALKANES Flashcards
In how many steps do most reactions of organic compounds take place?
via a series of steps
How can you predict the steps that most organic compound reactions take?
by thinking about how electrons are likely to move
What can looking at how electrons are likely to move in organic compound reactions help you understand?
understand why reactions take place as they do
What are nucleophiles- what do they do?
reagents that attack + form bonds with positively or partially positively charged carbon atoms
What charge does a nucleophile have?
negatively charged or has an atom with a slightly negative charge
What does a nucleophile have? (electrons)
lone pair of electrons
What can a nucleophile use its lone pair of electrons to do?
form a covalent bond
On a nucleophile where is the lone pair situated?
situated on an electronegative atom
So in organic chemistry what is a nucleophile?
species that has a lone pair of electrons with which it can form a bond by donating its electrons to an electron deficient carbon atom
What are some common nucleophiles? (3)
hydroxide ion, -:OH
ammonia, :NH3
cyanide ion, -:CN
What will nucleophiles do to the halogen in halogenoalkanes?
replace the halogen in a halogenoalkane
What is the reaction called when a nucleophile replaces the halogen in a halogenoalkane?
nucleophilic substitution
What does a reaction mechanism describe?
route from reactants to products via a series of theoretical steps
What may reaction mechanisms involve?
short-lived intermediates
What are curly arrows used to show?
show how electron pairs move in organic reactions
Where is the lone pair of electrons of a nucleophile attracted towards?
positively charged carbon atom
What is the halide ion originally from the halogenoalkane called?
leaving group
What does the rate of substitution with the halogenoalkane depend on?
the halogen
Why are fluoro-compounds unreactive?
due to strength of the C-F bond
How does the rate of reaction change going down the halogen group and why?
rate of reaction increases as the C-X bond strength decreases
At what condition does the reaction between a halogenoalkane and hydroxide ion occur very slowly?
room temperature
What is done to speed up the reaction between a halogenoalkane and hydroxide ion?
warm the mixture
Do halogenoalkanes mix well with water?
no
As halogenoalkanes don’t mix well with water, what is added during the reaction with halogenoalkanes and hydroxide ions?
ethanol used as solvent in which halogenoalkane and aqueous sodium ( or potassium) hydroxide both mix
What is the reaction between the halogenoalkane and hydroxide ion known as?
hydrolysis reaction
What happens when halogenoalkanes are warmed with an aqueous alcoholic solution of potassium cyanide?
nitrile formed
What does a nitrile have an extra of in comparison to the starting halogenoalkane?
one extra carbon in the chain than the starting halogenoalkane
What is the nitrile formed having one extra carbon than the starting halogenoalkane useful for?
useful if you want to make a product that has one carbon more than the starting material
Under what condition is a reaction of halogenoalkanes with an excess concentrated solution of ammonia in ethanol happen?
under pressure
What does a reaction of halogenoalkanes with an excess concentrated solution of ammonia in ethanol produce?
amine, RNH2
Why is ammonia a nucleophile? (2)
it has a lone pair of electrons that it can donate
nitrogen atom has a slightly negative charge
What is the charge of the ammonia nucleophile?
neutral
As the ammonia nucleophile is neutral what must be lost to form the neutral product, amine?
a proton, H+ must be lost
What happens to the H+ which is lost when amine is to be produced in a reaction between a halogenoalkane and ammonia nucleophile?
H+ ion reacts with a second ammonia molecule to form an NH4+ ion
Why are nucleophilic substitution reactions useful?
they’re a way of introducing new functional groups into organic compounds
What can halogenoalkanes be converted into due to nucleophilic reactions? (3)
alcohols
amines
nitriles
Order of what halogenoalkane can be turned into after primary amine?
halogenoalkane -> primary amine -> secondary amine -> tertiary amine
Order of what halogenoalkane can be turned into after alcohol?
halogenoalkane -> alcohol -> aldehyde -> carboxylic acid
Order of what halogenoalkane can be turned into after nitrile?
halogenoalkane -> nitrile -> primary amine OR carboxylic acid
