Haloalkanes Flashcards
Electronegativity definition
Power or an atom to attract the 2 elections in a covalent bond
3 factors effect ion electronegativity
Number of protons
Atomic radius
Shielding
How does number of protons affect electronegativity?
Stronger attraction between negative electrons in bonding pair and positive nucleus
How does atomic radius affect electronegativity ?
Closer the bonding pair to nucleus stronger the attraction
How does shielding affect electronegativity ?
More shells between bonding pair and nucleus, weaker attraction
Electron negativity down a group
Decreases
Explaination for electronegativity down a group
- atoms bigger
- more shielding
- weaker attraction between bonding pair and nucleus
- decreases
Electronegativity across a period
Increases
Explaination for electronegativity across a period
- atoms smaller
- more protons
- stronger attraction between bonding pair and nucleus
When does a non-polar covalent bond happen?
Two atoms in covalent bond have same electronegativity
When do polar covalent bonds happen?
Two atoms in covalent bond have different electronegativity
What is a non-polar covalent bond?
Covalent bond where 2 electrons are shared equally
What is a polar covalent bond?
Covalent bond where the 2 electrons are not shared equally
The more electronegative the greater the electron share
What is a bond dipole moment?
A measure of the strength + direction of the polarity in the bond
What does the bigger difference in electronegativity mean for bond dipole moment?
The bigger the bond dipole moment
3 things that determine electronegativity
- Nuclear charge
- Distance between nucleus + outer electron shell
- shielding by inner electron shells
Electronegativity across a period
Increases
- more protons = stronger nuclear charge
- smaller atomic radius
- stronger attraction between nucleus + outer electron shell
Electronegativity down a group
Decreases
- more shielding
- larger atomic radius
- weaker attraction between nucleus + outer electron shell
bond polarity definition
Unequal sharing or electrons between atoms rhat are covalently bonded
What is charge separation referred to as?
Dipole
Test for polarity
Balloon next to tap
3 types of halogen Alkanes
Primary
Secondary
Tertiary
What are the haloalkane types dependant on?
Bonding in the carbon atom to which the halogen atom is bonded to
What do bond enthalpies show?
Bond strongness
How are halogen allowances formed?
When a halogen takes place of hydrogen in an alkane
General halogen alkanes formula
CnH2n+1 (R-X)
What can haloalkanes be used for?
Solvents (dry cleaning)
Refrigerants
Pesticides
What is the ozone layer beneficial for?
it filters out mush of the suns harmful UV radiation
What does CFCs stand for?
Chloroflurocarbons
What do man made CFCs do?
Cause a hole in ozone lay a
What do chlorine free radical atoms do?
Catalyse the decomposition of ozone
Cl. free radical equation
Cl. + O3 -> ClO. + O2
ClO. + O3 -> 2O2 + Cl.
2O3 -> 3O2
What does regenerated Cl radical mean?
Means 1 Cl radical could destroy many thousands of ozone molecules
What bond is not affected by UV?
C-F
Why is c=c bond not 120 degrees?
Higher density so repels H electrons
What is a Z isomer?
Together
What is an E isomer?
Opposite
What is hydrolysis?
Splitting of a molecule using water
What is the reactivity of the C-X bond?
- C-X bond broken when haloalkane reacts
- reactivity depends on how easy C-X bond is to break
What 2 factors determine how easy C-X bond is to break?
- C delta + - X delta - bond polarity
- C-X bond enthalpy
What results in a electron - deficient carbon?
More electronegative halogen removes charge from carbon it is bonded to
What is electron - deficient carbon vulnerable to?
Vulnerable to attack by electron-rich reagents called nucleophiles
What would we expect more reactive electronegative halogens to give?
More reactive haloalkanes
What is the deciding factor for rate of hydrolysis?
Bond enthalpy
Bond enthalpies from strongest to weakest
C-F C-H C-Cl C-Br C-I
What will be more reactive is the bond polarity is important to the reaction?
R-F
What will be more reactive is bond enthalpy is important to the reaction?
R-I
What happens in a nucleophilic substitution reaction in hydrolysis?
A nucleophilic attacks a polar molecule + kicks out a functional group + settles itself down in its place
General equation for nucleophilic substitution of halogen alkane
CH3CH2X + Nu- -> CH3 CH2 Nu+ X-
What are the 3 nucleophiles
OH- (alcohol)
CN- (nitrile)
NH3- (amines)
Hydrolysis of haloalkane method
Put test tubes of haloalkane + ethanol in hot water bath add silver nitrate White = chloride Cream = bromide Yellow = iodide
What does R replete sent in nucleophilic substitution?
Alkyl group
What does X represent in nucleophilic substitution?
Any halogen
What does mechanism of nucleophilic substitution depend on?
Depends on C-X bonds strength
What is a nucleophile?
A particle with a lone pair of electrons which can donate to form a bond
Nucleophilic aubstitution steps
1) halogenoalkane undergoes nucleophilic substitution
2) lone pair of electrons on nucleophile attracted to electron deficient carbon
3) curly arrows show movement of pair of electrons
4) nucleophile causes electron in C-X bond to repel toward more electronegative halogen
5) forms halide ions
Free radical 3 steps
First propagation step
Second propagation step
Termination
Why do we use HFCs and not CFCs?
CFCs attached ozone layer + thinned down
Structural isomer definition
Molecules with same molecular formula but different structures
Acids, bases + alkali roles in elimination reaction in haloalkanes
Acid-proton donator
Base-proton acceptor
Alkali-soluble base
What does nucleophilic substitution with haloalkane form?
Alcohol
What happens when an OH- acts as a base?
Removes H+ from the haloalkane
Elimination rather than substitution
Conditions for elimination
- heat
- ethanol as a solvent (no water present)
- concentrated potassium hydroxide
