Properties of Hydrocarbons and Functional Groups

Flashcards covering electronegativity and bond types, molecular polarity, intermolecular forces, hydrophilicity versus hydrophobicity, hydrocarbon classes, alkane physical properties, and a wide range of common organic functional groups with their naming conventions.

What type of bond is formed when the electronegativity difference between two atoms is less than 0.5?

A non-polar covalent bond.

At what electronegativity difference range is a bond considered polar covalent?

When the electronegativity difference is between 0.5 and 2.0.

When the electronegativity difference exceeds about 2.0, what kind of bond is most likely?

An ionic bond.

Are C–H bonds considered polar or non-polar?

Non-polar.

What physical quantity measures overall molecular polarity?

Dipole moment (μ).

How is the dipole moment of a molecule determined?

By the vector sum of all individual bond dipoles and lone-pair contributions.

Why is CO2 non-polar even though it contains polar C=O bonds?

The two bond dipoles are equal and oriented in opposite directions, cancelling each other out.

Give an example of a molecule with a net dipole despite having several identical polar bonds.

CHF3 (trifluoromethane) is polar because its bond dipoles do not cancel.

What intermolecular force exists between all molecules, polar or non-polar?

London (dispersion) forces.

Which intermolecular force arises from attractions among permanent dipoles of polar molecules?

Dipole-dipole forces.

Define a hydrogen bond in organic chemistry.

An attractive interaction between a hydrogen bonded to an electronegative O or N and an unshared electron pair on another O or N.

Give two biological examples where hydrogen bonding is crucial.

Maintaining enzyme shape and stabilising the DNA double helix.

What does the term hydrophilic mean?

‘Water-loving’; substances that contain ionic charges or polar –OH groups and can hydrogen-bond with water.

Why are alkanes classified as saturated hydrocarbons?

Every carbon in an alkane has the maximum possible number of hydrogens; all bonds are single.

Name the four main classes of hydrocarbons.

Alkanes, alkenes, alkynes, arenes (aromatic hydrocarbons).

How does the presence of a C=C double bond change the classification of a hydrocarbon?

It becomes an alkene (an unsaturated hydrocarbon).

What general trend is observed for boiling and melting points of straight-chain alkanes as molecular weight increases?

Both boiling and melting points increase with increasing molecular weight.

How does branching affect the boiling point of an alkane?

More branching lowers the boiling point because of decreased surface area and weaker dispersion forces.

Are alkanes soluble in water? Why or why not?

No; alkanes are non-polar and cannot form strong interactions with polar water molecules.

State the ‘like dissolves like’ principle using alkanes as an example.

Non-polar alkanes dissolve in other non-polar solvents (e.g., toluene or diethyl ether) but not in polar solvents like water.

What is a functional group?

An atom or group of atoms within a molecule that shows a characteristic set of predictable physical and chemical behaviours.

List four reasons functional groups are important in organic chemistry.

They determine chemical reactivity, influence physical properties, provide a basis for classification, and form the foundation for systematic nomenclature.

Which functional group defines alcohols?

The hydroxyl group (–OH) attached to a saturated carbon.

What suffix is used in IUPAC names for alkenes?

-ene.

What functional group characterises aldehydes?

A carbonyl group bonded to at least one hydrogen (-CHO).

Which suffix indicates a ketone in IUPAC nomenclature?

-one.

Give the functional group and suffix for carboxylic acids.

Carboxyl group (-COOH); suffix “-oic acid.”

What functional group is present in an ester?

A carbonyl carbon bonded to an OR group (-COOR).

How are amides structurally identified?

A carbonyl carbon bonded to a nitrogen (-CONR2).

What suffix is assigned to nitriles?

-nitrile (or ‑carbonitrile).

Define an amine and give its naming suffix.

A compound with one or more alkyl groups attached to nitrogen; suffix “-amine.”

What functional group is characteristic of sulfides?

A sulfur atom singly bonded to two carbon atoms (R-S-R).

Which functional group contains an S–S bond?

Disulfides (R-S-S-R).

What is the difference between a thiol and an alcohol?

In a thiol the oxygen of an alcohol is replaced by sulfur (R-SH).

Give the functional group found in sulfoxides.

A sulfur doubly bonded to oxygen and singly bonded to two carbons (R-S(=O)-R).