Halogenoalkanes Flashcards
what are halogenoalkanes?
organic compounds containing halogen atoms such as Fluorine, Chlorine,Bromine and Iodine.
what is the general formula of halogenoalkanes?
CnH2n+1
what are primary, secondary and tertiary halogenoalkanes?
primary-
contain 1 alkyl group bonded to the carbon atom that the halogen is bonded to, minor product.
secondary-
contain 2 alkyl groups bonded to the carbon atom that the halogen is bonded to, medium major product.
tertiary-
contain 3 alkyl groups bonded to the carbon atom that the halogen is bonded to, major product.
explain the polarity of halogenoalkanes?
C-X bonds have different electronegativity , the C-X bond is polar. the electrons in the covalent bond are held closer to the halogen atom. this makes the halogen partially negative (δ-) and a partial positive charge (δ+) on the carbon atom, creating a dipole.
this polarity makes halogenoalkanes more reactive than alkanes.
what forces and interactions do halogenoalkanes consist of?
dispersion forces and dipole-dipole interactions
explain the trend in polarity within halogenoalkanes?
polarity increases as you go up the halogen group.
explain the solubility of halogenoalkanes?
insoluble,
due to the non-polar R groups (alkyl groups) as they form van der waal forces
explain how chain length affects boiling point of halogenoalkanes?
longer chain= higher boiling point
- because van der waal forces are increased with chain length meaning that there is more electrons present meaning it is harder to overcome these bonds and there is a larger surface area meaning that there is more points where van der waal forces can form.
explain how branching affects boiling point of halogenoalkanes?
branching= reduces boiling point
- van der waal forces are weaker, less surface area of contact even if there are the same numbers of electrons.
what affect does the halogen group have on the boiling point of halogenoalkanes?
increases down the group
- halogen is larger as there is more electrons, stronger van der waal forces.
list all the halogens in order of highest bond enthalpy to weakest.
C-F
C-Cl
C-Br
C-I
what does bond enthaply mean?
the higher the bond enthaply the harder it is to break the bond between the C-X
what is nucleophile?
highly negative, electron pair donors. possess at least one lone pair of electrons. not necessary to have a negative charge. attracted to slightly positive carbon (δ+).
what are the nucleophiles?
Hydroxide ion (OH⁻)
Cyanide ion (CN⁻)
Ammonia (NH₃)
Water molecule (H₂O)
which one of those 4 is the weakest?
Water molecule (H₂O)
explain the mechanism of nucleophilic substitution.
the nucleophile uses its lone pair to provide electrons for a new bond.
the halogen is then displaced - carbon can only have eight electrons in outer shells.
what is elimination reaction?
when a halogenoalkane is heated to high temperatures under alcoholic conditions, elimination occurs.
what base is used in elimination reaction?
Hydroxide ion (OH⁻), this removes the H+ ion from the halogenoalkane.
what are the reagents needed for this mechanism?
potassium or sodium hydroxide.
why must there be no water in the potassium (or sodium) hydroxide that is being dissolved in ethanol?
potassium reacting with water creates heat, which causes pressure which can lead to an explosion.
explain the mechanism of an elimination reaction.
the base attacks the adjacent hydrogen to the carbon which has the halogen bonded to it, this then breaks the bond between the hydrogen and carbon, creating a double bond. then the halogen removes from the carbon.
what are the byproducts of this reaction?
H2O and KX or NaX (where X is the halogen)
what is formed after the reaction?
an alkene, a type of molecule that has a special bond called a double bond between two carbon atoms. this double bond makes alkenes different from simpler molecules like alkanes.
what is ozone?
ozone is formed naturally in the upper atmosphere, is beneficial because it absorbs ultraviolet radiation.
