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Haloalkanes
The Haloalkanes and their reactions and properties
| Question | Answer |
|---|---|
| Make two comments about the solubility of Haloalkanes: | They are not soluble in Water (as water prefers to make Hydrogen bonds with itself and not Dipole-Dipole with the Haloalkane). An organic Solvent is required (such as an Alcohol). |
| What happens to the boiling point of a Haloalkane as the chain length increases: | The BP will increase as there is a greater straight chain mass which allows for stronger VDW forces. |
| What happens to the boiling point of a Haloalkane as it branches more? | The Boiling point will decrease as the molecules are unable to compact together as much, which reduces the effect of the the VDW forces between molecules. |
| What happens to the Boiling point of the Haloalkanes going down the G7 of Halogens? | They boiling point will increase as it will have greater mass going down the group, which increases the effect of the VDW forces. |
| Which of the halogens is the most reactive in the Haloalkane context? | The Iodo-Haloalkanes are the most reactive as the bond between C-I is weakest as the Iodine is a large atom, with its electrons far from the nucleus with weak attraction due to shielding. |
| What is the name of the reaction mechanism when a Haloalkane reacts with a Nucleophile? | Nucleophilic Substitution (Sn2). |
| What is a Nucleophile? | It is a species which will donate a pair of electrons in a reaction to form a bond with an electrophile. |
| What is the first step of Nucleophilic substitution? | A lone pair of electrons on the Nucleophile will be attracted the delta positive carbon atom as the electronegative halogen is attracting the electrons in the bond. |
| What is the second step of Nucleophilic Substitution? | The lone pair of electrons will bond with the Carbon Atom and the Electron pair from the C-X bond will move to the Halogen, causing the Halogen to become a Halide Ion (X-). |
| What are three of the common Nucleophiles used for Nucleophilic Substitution? | Cyanide Ion, Ammonia and Hydroxide Ion. |
| Why are the Ammonia, Hydroxide Ion and the Cyanide Ion called Nucleophiles? | They are very electron rich and have lone pairs of electrons which are able to be donated to delta positive atoms. They are very attracted to Positively (or slightly positively) charge atoms. |
| Give the general equation of a Nucleophilic Substitution reaction with a Haloalkane: | RCH-X + Nu- ---> RCH-Nu + X- Haloalkane + Nucleophile ---> New Hydrocarbon alkane + Halide Ion. |
| What is formed when a Nucleophilic Substitution reaction happens between a Haloalkane and the Cyanide Ion? | A Nitrile with a carbon chain length +1 carbon from the original Hydrocarbon Chain. |
| What is formed when a Nucleophilic Substitution reaction happens between a Haloalkane and Hydroxide Ion: | An Alcohol will be formed. |
| What is formed when a Nucleophilic Substitution reaction happens between a Haloalkane and Ammonia? | A primary Amine (which can be used to form Secondary and Tertiary amines) |
| What is the OH ion acting as in the Elimination reaction? | A Base, as it is a Proton acceptor. |
| What are the products of an Elimination reaction between OH and Haloalkane? | X- + Alkene + H2O. |
| What are two of the factors that can affect if a reaction will be Sn2 or E2? | If the Hydroxide is heated, dissolved in Alcohol or it is a Tertiary Haloalkane, Elimination is likely. If the OH solution is cold, dissolved in water or it is a primary Haloalkane, Sn2 is likely. |
| Step 1 of E2: | A lone pair of electrons on the OH ion forms a bond with one of the Hydrogen atoms in the Haloalkane. |
| Step 2 of E2 reaction: | The electron pair in the bond between the H-C moves to form a C=C as one of the carbons is slightly positive from having formed a bone with a Halogen. |
| Step 3 of E2 reaction: | The Electron pair between then Halogen and Carbon moves to the Halogen and the Halogen is the leaving group. An Alkene, Halide ion and Water are formed. |
| Which conditions and type of Haloalkane favour Elimination? | Non-Primary Haloalkanes and Hot, Ethanolic OH solution favour Elimination. |
| What conditions and type of Haloalkane favour Substitution? | Cold, Aqueous solution of OH ions and Primary Haloalkanes favour Substitution. |
| Define Free Radical: | An unstable species with an unpaired valance electron, making it highly reactive. |
| What are the three stages of a Free Radical Substitution reaction? | Initiation, Propagation and Termination. |
| What is the Free Radical Substitution an example of? | A Chain Reaction! One stage sets of another which results in another. |
| What happens during the Initiation stage? | Chlorine Radicals are formed from using a Quantum of UV light to break the Chlorine bonds. |
| What happens during the Propagation stage? | The Chlorine radicals remove a Hydrogen Atom from the Hydrocarbon, forming HCl and a Hydrocarbon Free Radical, which is also highly reactive. The Hydrocarbon Radical then reacts with Chlorine to form a Chlorine Radical and a molecule of Haloalkane. |
| What are three possible steps in termination? | 1) Chlorine molecule formed from 2 Chlorine radicals. 2) A Haloalkane formed from A Chlorine Radical and a Hydrocarbon Radical. 3) Another Hydrocarbon formed from two Hydrocarbon radicals. |
Created by:
mjwilson1988
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