Halogenoalkanes

Question 1

prefixes for each halogen in halogenoalkanes

Answer 1

fluoro
chloro
bromo
iodo

Question 2

how to classify if a halogenoalkane is primary secondary or tertiary

Answer 2

primary halogenoalkanes is when a halogen is attatched to a carbon that is attatched to only one alkyl group

2 alkyles is secondary

3 alkyles tertiary

Question 3

what is a nucelophile

Answer 3

an electron rich species that can donate a pair of electrons

Question 4

what is a nucleophilic reaction

Answer 4

one in which uses a nucleophile

Question 5

what nucleophile is used in the reaction to form an alcohol from a halogenoalkane

Answer 5

OH-

Question 6

what conditions for the reaction to form an alcohol from a halogenoalkane

Answer 6

NaOH and ethanol in water bath

Question 7

what determines the rate of reaction in a reaction to form an alcohol from a halogenoalkane

Answer 7

the type of halogen

the stronger the c-x bond the slower the rate therefore cl has slowest rate

Question 8

why is the c-cl bond strongest compared to other halogens

Answer 8

decreased covelant radius = greater attraction to electrons in the covelant bond

Question 9

why is water not used in the reaction to form an alcohol from a halogenoalkane

Answer 9

it is a vewry weak nucleophile but would eventually work just take a long time

Question 10

why do we get a precipitate in the reaction to form an alcohol from a halogenoalkane after adding silver nitrate

Answer 10

silver ions react with halide to form a silver halide precipitate

Question 11

method with reagents and conditions for the formation of nitriles

Answer 11

using nucleophile - CN-
potassium cyanide is heated under reflux with the halogenoalkane
product is a nitrile

the carbon chain on the product is extended by 1 compared to the reagent

Question 12

method for the formation of primary amines by reaction with ammonia and reagents and conditions

Answer 12

nucleophile - NH3
heated under pressure with the primary halogenoalkane

primary amine is formed

Question 13

method for the formation of alkenes ffrom halogenoalkanes

Answer 13

heated under reflux with ethanolic NaOH

c-x bond breaks heterolytically forming X- and the alkene

halogeno + NaOH –> Alkene + water + Na X

Question 14

what occurs in a nucleophilic substitution reaction

Answer 14

a nucleophile attacks a carbon atom which carries a partial positive charge

an atom with partial negative will be replaced by the nucleophile

Question 15

mechanism for a nucleophilic substitution with an OH nucleophile

Answer 15

OH with curly arrow to carbon. the bond between this carbon and halogen then has curly arrow from middle to halogen.

makes an alkane and halogen

Question 16

mechanism for nucleophilic substitution with ammonia

Answer 16

lone pair on ammonia attacks the partially positive carbon so curly arrow towards that from ammonia

curly arrow from c-x bond to x

left with CH3NH3

ANOTHER molecule of NH3 has curly arrow towards hydrogen of one of the hydrogens bonded to the NH3 group

curly arrow from n-h bond to n

forms an amide ion and ammonium and halogen

Question 17

why is excess ammona needed in the nucleophilic reaction

Answer 17

prevent further substitution and favor the formation of a primary amine

Question 18

what compound can be used to measure the rate of hydrolysis in halogenoalkanes

Answer 18

acidified aqueous silver nitrate

Question 19

what is the method to measure the rate of hydrolysis of halogenoalkanes

Answer 19

set up test tubes in 50 degree water bath

add ethanol and acidified silver nitrate

add a few drops of chloroalkane, chlorobromide, chloroiodide

start stopwatch

time how long it takes for a precipitate to form in each

can also be used to identify the reactivity of a halogenoalkane

Question 20

what precipitates form with the different halogenoalkanes

Answer 20

chlorides - white
bromides - cream
iodide - yellow

Question 21

what is the fastes precipitate formed in the addition of silver nitrate to halogenoalkanes and why

Answer 21

silver iodide is the fastest ( fastest nucleophilic substitution)

because the c-i bond has the lowest bond enthalpy ( due to iodides increased shielding)

this means it is the easiest to break and will cause I- ions to form the fastest

Question 22

why doest a fluoro alkane produce a precipitate with silver nitrate

Answer 22

silver fluoride that would be formed is soluble

this confirms that it is the least reactive

Question 23

what is the fastest rate of hydrolysis - primary , secondary, teriary

Answer 23

tertiary reacts fastest because the rate of hydrolysis is determined by the use of either SN1 or SN2 reaction mechanism

tertiary halogenoalkanes favour SN1 reactions

Question 24

what are the two different ways a nucleophilic substitution reaction can occur

Answer 24

SN1 and SN2

Question 25

what do primary vys tertiary halogenos favour different ways a nucleophilic substitution

Answer 25

tertiary - SN1 Primary - SN2

Question 26

what is the etymology of SN1

Answer 26

s = SUBSTITUTION N = nucleophilic 1 = rate of reaction which is determined by the slowest step of the reaction

Question 27

mechanism of an SN1 reaction

Answer 27

C-X bond breaks heterolytically and the halogen leaves the halogenoalkanes as an x ion ( this is the slowest step of the reaction) this means curly arrow to the x an OH nucleophile can then curly arrow to attatch to the alkane resulting in a TERTIARY alcohol ( because this is a tertiary halogeno and an sn1 reaction)

Question 28

SN2 mechanism is it one step or two like SN1

Answer 28

one step

Question 29

mechanism of SN2

Answer 29

nucleophile donates e- to partially positive carbon forming a new bond (shown by curly arrow) at the same time the c-x bond is breaking and the halogen takes both electrons in the bond leaves a halogen and an alcohol this reaction has the transition state

Question 30

which haogenoalkane is the most likely to undergo substitution reactions

Answer 30

C-I as it breaks heterolytically very easily