Topic 6D - Halogenoalkanes (Organic Chemistry) Flashcards
Are Halogenoalkanes soluble?
No (they are slightly soluble)
Why are Halogenoalkanes only slightly soluble in water?
This is due to the fact the polar interaction between the water molecule and Halogenoalkane are weaker than the hydrogen bonding present in water. Additionally, Halogenoalkanes cannot form hydrogen bonds as they do not contain an H - F,O or N.
What are hydrogen bonds?
They are the strongest type of intermolecular force/bonding
How are hydrogen bonds formed?
When you have an H - F,O or N in a molecule it is able to form hydrogen bonds. The hydrogen is attached directly to an extremely electronegative
element causing the hydrogen to gain a delta + charge. Each of the elements that the Hydrogen is attached to also has at least one ‘active’ lone pair. As the delta + hydrogen is formed it becomes extremely attracted to the delta - element of another molecule, for example; water.
What is a primary Halogenoalkane?
The halogen atom is attached to the first carbon in the chain (the Hl - C bond has one carbon attached to the bonding carbon)
What is a secondary Halogenoalkane?
The halogen atom is attached to a carbon that is not on the end of the chain but not at a branch (the Hl - C bond has two carbons attached to the bonding carbon)
What is a tertiary Halogenoalkane?
The halogen atom is bonded to a carbon at a branch in the chain (the Hl - C bond has three carbons attached to the bonding carbon)
Do the isomers 1-bromobutane, 2-bromobutane, and 2-bromo-2-methylpropane decrease in boiling point as you go down them?
Yes
Why do the isomers 1-bromobutane, 2-bromobutane, and 2-bromo-2-methylpropane decrease in boiling point as you go down them?
This is because as the Halogenoalkane becomes more branched as the surface area of it decreases (for the same number of electrons in the molecule) which in turn decreases the strength of London dispersion forces as there is a smaller area over which they can form. Therefore the intermolecular forces are easier to overcome in branched molecules.
What are London Forces?
The weakest type of intermolecular force.
How do London Forces form?
In molecules their are constant electron fluctuations that cause instantaneous dipoles to form within them leaving the molecule with a delta positive and negative side. This dipole can then induce another dipole ( an induced dipole ) into another molecule.
Do Halogenoalkanes have higher or lower boiling points that alkanes? Why?
They have higher boiling points as the polarity of the carbon - halogen bond present leads to stronger intermolecular forces
What is the definition of electronegativity?
The tendency of an atom to attract a bonding pair of electrons in a covalent bond
What dipoles are present in Halogenoalkanes?
There will be a dipole in the C- X bond ( halogen ) the X will have a delta - pole and the C will have a delta + pole.
What is a nucleophile?
A nucleophile is an ion or compound with a negative charge and a lone pair of electrons (electron donating) that has a tendency to attack atoms which are electron deficient, with a partially positive charge for example; Hydroxide ion, Water Molecule, Cyanide ion, Ammonia molecule
The carbon with a delta + charge in halogenoalkanes is susceptible to be attacked by…
Nucleophiles such as; OH-, NH3, H2O
Halogenoalkane + potassium Hydroxide -> Alcohol + potassium Halide is what type of reaction?
Nucleophillic substitution
What reagant is need for the Nucleophillic substitution reaction between a Halogenoalkane and KOH/ NaOH -> Alcohol + Metal Halide?
Aqueous NaOH or KOH
What conditions are needed for the Nucleophillic substitution reaction between a Halogenoalkane and KOH/ NaOH -> Alcohol + metal halide?
Heat under reflux
What is the nucleophile in the reaction of Halogenoalkane and KOH/ NaOH -> Alcohol + metal halide?
OH-
How can you test for the presence of Halide ions on the reaction of Halogenoalkane and KOH/ NaOH -> Alcohol + metal halide?
By adding silver nitrate (AgNO3) to the solution which will form a precipitate
Which group is the ‘leaving group’ in the reaction of Halogenoalkane and KOH/ NaOH -> Alcohol + metal halide?
The Halogen (Chlorine, Bromine, Iodine)
What is the definition of a substitution reaction?
It is a chemical reaction where and atom or functional group of a molecule is replaced by another atom of functional group
What is the definition of a ‘leaving group’?
The atom or group of atoms substituted out of the molecule that takes a pair of electrons with it.
What are the colours of the precipitates that from when Silver Nitrate is added to a solution that contains a Halide?
Chlorine - White precipitate of Silver Chloride
Bromine - Cream precipitate of Silver Bromide
Iodine - Yellow precipitate of Silver Iodide
What does the mechanism of the Nucleophillic substitution of Halogenoalkanes depend on?
Whether the Halogenoalkane is primary, secondary or tertiary
What Nucleophillic substitution reaction mechanism do primary/ secondary Halogenoalkanes use?
Sn2
S - substitution
N - Nucleophillic
2 - number of species acting in the initial stage of the reaction
What Nucleophillic substitution reaction mechanism do tertiary/ secondary Halogenoalkanes use?
Sn1
S - substitution
N - Nucleophillic
1 - number of species acting in the initial stage of the reaction
How many stages does Sn2 have?
1