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23 Cards in this Set
- Front
- Back
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Describe an SN1 reaction |
A halogen spontaneously breaks off from a halogenoalkane (slow step), after which a nucleophile takes its place (fast step), bonding with the carbocation. Happens for tertiary halogenoalkanes. |
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Describe an SN2 reaction |
A nucleophile "attacks" the positive (due to polarity) carbon in a halogenoalkane, forming a transition state (the carbon has 5 bonds). The halogen then breaks off. Happens for primary halogenoalkanes. |
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Describe the oxidation of a secondary alcohol |
Oxidised by warming with acidified potassium dichromate (VI), into a ketone, which cannot be oxidised further. Colour change: Orange to Green |
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Describe the oxidation of a primary alcohol |
Oxidised by warming with acidified potassium dichromate (VI), into an aldehyde, which can be further oxidised into a carboxylic acid. Colour change: Orange to Green |
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Discuss the effect of the nucleophile in nucleophilic substitutions |
Anions tends to be more reactive than their neutral counterpart (OH- is more reactive than H2O) |
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Define nucleophilic substitution |
Reagents with a non-bonding pair of electrons "attacking" the electron-deficient atom in a polar bond. |
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Describe the trend in boiling points for homologous series |
As the length of the carbon chain increases the boiling point also increases, but as the degree of branching of the chain increases, the boiling point decreases. |
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Describe the solubility of organic compounds |
If the functional group is non-polar, the compound will only dissolve in non-polar solvents. If it is polar, the compound will become less soluble in polar compounds the longer the chain becomes. |
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Define bromination |
An addition reaction where Br2 reacts with an alkene to form a dihalogenoalkane. Colour change: Orange to colourless Used to test for alkenes |
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Define hydration |
The addition of steam (H2O) to an alkene produce an alcohol. |
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Define hydrogenation |
The addition of H2 to an alkene to produce an alkane. Used to produce margerine from vegetable oils |
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Define esterification |
A condensation reaction where an alcohol and a carboxylic acid react and form an ester and water. |
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Describe the effect of solvent in nucleophilic substitutions |
A polar solvent supports the breakdown of the halogenoalkane in SN1 reactions, while a non-polar solvent favours SN2 reactions which involve a transition state. |
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Describe the mechanism of electrophilic addition to an alkene |
The double bond of the alkene has a high electron density, which attracts the less electronegative molecule in a polar bond, causing it to break off and bond to one of the carbons in the double bond. This in turn leaves a carbocation which attracts the now negative ion left after the polar molecule broke. The same thing happens to non-polar molecules as a result of induced dipoles in NON-POLAR substances. |
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Distinguish between fish hooks and curly arrows |
Curly arrows are used to show the movement of an electron pair. Fish hooks are used to show the movement of a single electron. |
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Explain Markinov's rule |
The intermediate state of the addition of hydrogen halide addition to alkenes can have a primary, secondary, or tertiary carbocation (the carbon that is positively charged after the double bond has been lost to the electron). The tertiary carbocation will be the most stable, since the three carbons push electrons towards the carbocation, followed by the secondary and tertiary carbocations respectively. Thus, a tertiary carbocation will be preferred as an intermediate state, and will lead to the major product. |
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Explain the nitration of benzene |
Electrophilic substitution: A mixture of concentrated nitric acid and concentrated sulfuric acid at 50 degrees. H2SO4 + HNO3 --> H2NO3+ + HSO4- After which H2NO3+ splits into water and NO2+ (electrophile) The electrophile is attracted to the delocalised pi bond of the benzene, and with considerable activation energy to break the pi bond partially, NO2+ attaches to one of the carbons. The carbon the loses its H+ and those electrons recomlete the "circle". The H+ then combines with HSO4- to reform the catalyst. |
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What compounds can be used for reduction of carbonyl groups? |
LiAlH4 (strong, needs aprotic solvent as it would react with water, then the reaction must be acidified to get the product) NaBH4 (weak, so can be used directly with protic solvent, but ineffective at reducing carboxylic acids) Hydrogen, in combination with a nickel, platinum, or palladium catalyst. |
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Describe the reduction of nitrobenzene |
1. Nitrobenzene is refluxed with tin and HCl NO2benzene + 7H+ + 6e- --> NH3+benzene + 2H2O 2. Addition of NaOH NH3+benzene + OH- --> NH2benzene + H2O |
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What is the difference between cis/trans and E/Z isomerism? |
Cis/trans: Whether the two subsituent groups (not hydrogen) are on the same or different sides of the double bond E/Z: Whether the highest priority (highest mass) subsituents on each of the carbons are on the same or different sides of the double bond. |
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List some reasons for the delocalised electron model for benzene |
1. The C-C bond lengths are all the same, which would not be true if some of them had double bonds. 2. The bond enthalpy for the double bond model would be higher. 3. Only one isomer exists for 1, 2- disubstitued benzene compounds. 4. Benzene is unwilling to undergo addition reactions. |
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What is the difference between enantiomers and diastereomers? |
Enantiomers are mirror images, whereas diastereomers are not. Enantiomers have the same physical properties, and the same chemical properties, except when interacting with other optical isomers. Diastereomers have different physical properties and different chemical reactivity. |
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Describe the properties of optical isomers |
They have a chiral centre with four different groups bonded to it. |
