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Alkane reactions
Organic Chem MCAT
| Question | Answer |
|---|---|
| What are the criteras for the boiling point? | Molecular Weight and Chain length (branched decreases boiling point), and intermolecular forces |
| What are the criterias for melting point? | Polarity and Symmetry (branched decreases melting point) |
| What are the products of the combustion of an alkene? | Carbon dioxide, water and heat |
| What is the most common alkane reaction? | Halogenation (hydrogens are replaced with a halogen) |
| What is the most important factor that determines the occurence of an alkane reaction? | Stability of the carbocation (Tertiary>secondary>primary) |
| What is the first category of reactions of Alkanes (alkyl halides)? | Nucelophilic substitution (SN1 AND SN2) |
| What are nucelophiles? | Electron rich species that attract positively charged nucleus (exactly similar to lewis bases) |
| What are electrophiles? | Electron deficient species that love electrons |
| What features distingushes two nucelophiles? | If the nucelophiles have the same attacking atom, then the nuccleophilicity corresponds to basicity |
| What are protic solvents? | Solvents such as water and alcohol where larger atoms tend to be better nucleophiles |
| What are aprotic solvents? | Solvents without protons where nucelophilicity correspond to basicity. |
| What are leaving groups? | Good leaving groups are weak bases such as larger anions or neutral species (as we go down the periodic table, size of the molecule increases) |
| What is a SN1 reaction? | Dissociation of a molecule in to a carbocation following a good leaving group, and then the combination of a carbocation with a nucleophile |
| What is the rate of a SN1 reaction? | The formation of the carbocation is the rate limiting step. And, hence it is a first order reaction (rate does not depend on the nucelophile) |
| What are the characteristics of a SN1 reaction? | Highly substituted alkyl halides, polar protic solvents (stabilizes the intermediate state), and good leaving group) |
| What is a SN2 reaction? | WHn carbocation formation is impossible, then a nucelophile pushes its way in to the compund forming a pentacoordinate system, and displaces the leaving group in one step. |
| What are the characteristics of a SN2 reaction? | Strong nucleophile, and sterically unhindered substrate (primary or secondary substrates) |
| What is the rate of a SN2 reaction?? | Since the reaction depends on the concentrations of both the nucelophile and the leaving group, it is second order |
| What are the sterochemistry of substitution reactions? | In SN1 reactions, the sterochemistry of the products is lost as it becomes a racemic mixture while in SN2, if both the leaving group and the nucelophile have the same priority, then there is an inversion, otherwise not. |
| What are the three types of reactions that an alkane undergo? | Halogenation (Only with chlorine and bromine), Combustion and Pyrolysis (cracking with heat) |
Created by:
prijuvarghese
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