Organic Chemistry Flashcards
Explain low reactivity of alkanes
Relatively strong bonds, require a lot of energy. Low polarity of bonds, so electrophile/nucleophiles are poorly attracted
What is volatility
Measure of how easily a substance can turn into gaseous state. Volatility is overcoming intermolecular forces. High volatility = low boiling point.
Explain the influence of carbon chain on volatility
The longer a straight chain, the higher LDF forces, higher boiling point, therefore lower volatility. If there is a branched chain, LDF forces are weaker.
Explain the influence of functional groups on volatility
When highly polar functional groups interact with water, boiling point will be higher and volatility lower.
What is solubility
The extent to which the solute molecules are able to interact and form hydrogen bonds with water
What is solubility
The extent to which the solute molecules are able to interact and form hydrogen bonds with water
Explain the influence of the hydrocarbon skeleton on solubility
This part of the molecule is non-polar, so unable to form hydrogen bonds with water. Higher members of the homologous series are less soluble than lower members.
Explain the influence of the functional group on solubility
The smaller members of series with functional groups which form polar bonds with water (carboxylic acid, alchohols, and amines) are soluble in water. Aldehydes, ketones amides and esters are less soluble. Halogenalkanes, alkenes, alkanes and alkynes are insoluble.
Explain the trend in boiling points in a homologous series
The boiling point increases along molecules in a homologous series, because the boiling point increases with mass. As you go down a homologous series, more intermolecular forces (LDF) are at play, and therefore more energy is needed to break the bonds between molecules, increasing boiling point.
How can you test between an alkane and an alkene?
The difference is: saturated or unsaturated. Alkanes are saturated, as they have no double or triple carbon-carbon bonds. Testing can be done by adding bromine water. If when added to the substance, the bromine water loses its colour, it is unsaturated, as Bromine attacks the carbon double bond, replacing it with itself (halogenation), which is only possible if it is an alkene.
What are protic and aprotic solvents?
Both polar solvents. Protic solvents can form hydrogen bonds (Eg. ethanol, ammonia) Aprotic solvents cannot (dimethyl sulfoxide, propanone)
Why are SN1 reactions favored by protic polar solvents?
In step 1 (RDS) of SN1 reactions, two ions are formed (carbocation and negative halide ion). These ions are stabilised by the presence of protic solvents, the protic solvents solvate both ions effectively. Aprotic solvents would be ineffective at solvating the negative ions formed and would decrease the rate of SN1 reaction
Why are SN2 reactions favored by aprotic polar solvents?
The RDS of an SN2 reaction involves the attack of a negative ion (nucleophile). In an aprotic solvent, the nucleophile is not surrounded by solvent molecules and is free to attack the carbon atom. In a protic solvent, the nucleophile (negative ion) would be surrounded by solvent molecules and would not be effective.
What are factors effecting rate of nucleophilic substitution?
The halogen and nucleophile
How does the halogen affect rate of nucleophilic substitution?
Both the polarity of the C-X bond and the bond enthalpy. The C-I molecule is least polar, so it is expected that the nucleophile would be poorly attracted to the C atom and the rate would be slower. However, Because it has a low bond enthalpy, this is the overriding/dominating factor. Therefore, because the C-I bond takes the least energy to break, iodo-compounds have the fastest rate of nucleophilic substitution.
