Organic Chemistry Flashcards by Dominique Dizon

Explain hydrogen bonding in alcohols

Electronegative oxygen atom polarises the O-H bond. Creates a very high surface charge density on the hydrogen atom. Leads to strong intermolecular attractions. Lone pairs of electrons from oxygen atoms on different molecules

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Explain the volatility (tendency to evaporate) of alcohols

High melting and boiling points in comparison to molecules of similar molecular masses. They are less volatile than molecules of similar molecular mass due to hydrogen bonding

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Explain alcohol’s solubility/miscibility with water

Soluble as long as the alkyl group R is small. The OH group can form hydrogen bonds with water (like-like intermolecular forces). If the non-polar R group is too large, the hydrogen bonding in water would be disrupted so it does not dissolve

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Will aqueous solutions of alcohols have a lower or higher melting point than pure water? Why?

Lower - impurities always lower the melting point

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What are some uses of alcohols?

Drinks, antifreeze, biofuel

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Why and how are alcohols (especially diols) used as antifreeze?

Ethane-1,2-diol disrupts hydrogen bonding when dissolved in water

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What is the functional group for aldehydes?

C=OH

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What is the functional group of ketones?

C=O

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What is the functional group of carboxylic acids?

C=OOH

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What is the functional group of alcohols?

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What is the functional group of alkanes?

C-C (single bonds between carbon atoms) hydrocarbon

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What is the functional group of alkenes?

C=C (double bonds between two carbon atoms) hydrocarbon

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Structural isomers def

A compound with the same molecular formula but different structural formulae

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What is the catalyst needed for hydration of alkanes to make alcohols?

Acid - concentrated H3PO4 or H2SO4

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What is the monomer unit for polypropylene?

H              CH3
      \           /
n     C  =  C
      /           \
    H            H
(propene)

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What is the monomer unit for polyvinyl chloride (PVC)?

H            Cl
      \           /
n     C  =  C
      /           \
    H            H
(chloroethene)

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What is the monomer unit for polytetrafluoroethene (PTFE)?

F            F
      \           /
n     C  =  C
      /           \
    F            F
(tetrafluoroethene)

Homologous series def

A series of compounds with the same functional group but each subsequent member differs by CH2 (methylene unit)

What do curly arrows in electrophilic addition reactions represent?

The movement of a pair of electrons

Nucleophile def

Electron pair donators

Electrophile def

Electron pair acceptors

Why do free radical substitution reactions produce a mixture of organic products?

There is further substitution, there’s more than one termination step, substitution happens at different positions along the chain

What are two different ways to make ethanol? What are the equations?

Hydration of ethene: C2H4(g) + H2O(l) —> C2H5OH(aq)

Fermentation of sugar: C6H12O6(aq) -yeast-> 2C2H5OH(aq) + 2CO2(g)

Compare and evaluate the two methods of making ethanol

Hydration: Pos - higher percentage yield, no waste products. Neg - requires high pressures of 5-10 atmospheres as ethene is a gas, requires high temperatures of 350°C so energy is used for the heat
Fermentation: Pos - easy to do (can be done at home), makes more moles of ethanol. Neg - takes much longer, has waste products, requires temperatures of 30-40°C and anaerobic conditions

What are primary, secondary and tertiary alcohols oxidised to?

Primary: distil to aldehydes, reflux to carboxylic acids Secondary: reflux to ketones Tertiary: nothing

What is the test for aldehydes?

Fehling's solution gives a red precipitate

What is the test for carboxylic acids?

Sodium carbonate (solid or solution) effervesces

What reagent is used in oxidising alcohols?

Acidified potassium dichromate | K2Cr2O7/H+ (or specifically H2SO4)

What colour change will be observed when alcohols are oxidises with acidified potassium dichromate?

Orange to green (primary: colour changes rapidly, secondary: colour changes slowly)

Alkyl group def

Fragments of alkane molecules with one hydrogen missing eg The branches on branch chain alkanes (CnHn+1)

Chain isomerism

Only have a different carbon backbone e.g. shorter chain but more alkyl branches

Positional isomerism

Functional group is in a different position on the chain e.g. primary vs secondary vs tertiary alcohols, double bond in different position

Functional group isomerism

Have a different type of functional group e.g. cycloalkanes and alkenes

Describe the trend in volatility of alkanes

C and H have similar electronegativity's so bonds are non-polar and there are no permanent dipole moments. Hydrocarbons are volatile as it takes little energy to separate the molecules

Why are London forces stronger between unbranched chains of carbon atoms?

The contact surface area is greater

Viscosity def

The tendency for a liquid to resist flow

What do additions reactions with alkenes form?

With hydrogen to form alkanes, with halogens to form dihalo compounds, with hydrogen halides to form monohalo compounds, with steam to form alcohols, with bromine water to form 2-bromoethanol (ethene)

Describe electrophilic addition

Electrons in a double bond (in an alkene) move to the positive dipole. Both electrons from the bond holding the two atoms in the molecule together move to the negative dipole, breaking by heterolytic fission. Double bond is broken and there is a carbocation. ...

Describe the trend in viscosity in alkanes

Increases with length of carbon chain as longer chains have a greater tendency to become entangled. Branching decreases it.

Describe the trend in density in alkanes

Straight chains have a greater density than branched chains as they can pack together more closely and fit into a smaller volume

What is the difference between E & Z and cis & trans?

cis and trans - only two different substituents on a double bond (eg hydrocarbons, alkyl groups) E and Z - heaviest groups (Mr), can be substituents other than alkyls