Hydrocarbons

Hydrocarbons

one of the two general classifications of organic compounds consisting entirely of C and H atoms that are arranged and bonded in specific ways

Molecular Geometry

Factors Affecting the Physical and Chemical Properties of Organic Compounds:

• solubility changes according to the 3D arrangement of atoms in a molecule

Presence of Functional Groups

Factors Affecting the Physical and Chemical Properties of Organic Compounds:

• specific groups of atoms that are responsible for its reactivity and influences polarity

Number of Carbon Atoms and Branching

Factors Affecting the Physical and Chemical Properties of Organic Compounds:

• the higher the Carbon atoms, the less polar it is and the higher its boiling point

• the higher the branching of the carbon atoms, the more polar it is and the lower its boiling point

Intermolecular Force of Attraction (IMF)

Factors Affecting the Physical and Chemical Properties of Organic Compounds:

• Hydrogen Bonding > Dipole-Dipole Interactions > London Dispersion Factors

Aromaticity

Factors Affecting the Physical and Chemical Properties of Organic Compounds:

• compounds that are cyclic, conjugated, stable, planar, undergoes substitution reaction, and follows Huckel’s Rule (4n + 2 = pi-electrons)

Intermolecular Force of Attraction (IMF)

Physical States of Hydrocarbons:

• these physical states and properties are influenced by ______________.

higher

Physical States of Hydrocarbons:

• The Stronger the IMF, the ____________ the MP and BP

higher

Physical States of Hydrocarbons:

• the higher the presence of polar functional groups, the ________ the MP and BP

higher

the higher the number of carbon atoms, the _________ the MP and BP

lower

the higher number of branching, the ___________ the MP and BP

Anti-Aromatic

a compound that has all of the criteria for aromaticity except the Huckel’s Rule

Non-Aromatic

compound that follows the Huckel’s Rule but does not satisfy one criteria

Aliphatic Hydrocarbons

Classification of Hydrocarbons:

• hydrocarbons that does not contain aromatic rings

• can be linear, branched, or non-aromatic rings

Methane, Propane, and Cyclohexane

examples of aliphatic hydrocarbons

Aromatic Hydrocarbons

Classification of Hydrocarbons:

• contain benzene rings or similar conjugated rings systems

• highly stable due to aromaticity

Benzene and Toluene

examples of Aromatic Hydrocarbons

Acyclic Hydrocarbons

Classification of Hydrocarbons:

• open-chain structures that are straight or branched that can be saturated or unsaturated

Butane and Butene

examples of Acyclic Hydrocarbons

Cyclic Hydrocarbons

Classification of Hydrocarbons:

• closed-ring structures that can be aliphatic or aromatic

Cyclopentane and Benzene

examples of Cyclic Hydrocarbons

Saturated Hydrocarbons

Classification of Hydrocarbons:

• hydrocarbons that contain only single bonds

• also known as alkanes

Ethane and Propane

examples of Saturated Hydrocarbons

Unsaturated Hydrocarbons

Classification of Hydrocarbons:

• contains double or triple bonds

• can be alkenes or alkynes

Ethene, Butyne

examples of unsaturated hydrocarbons

Actively Unsaturated Hydrocarbons

Classification of Hydrocarbons:

• a term often used for alkynes and compounds with multiple reactive double/triple bonds

• highly reactive

Acetylene

example of actively unsaturated hydrocarbons

Solubility Test of Hydrocarbons in H2SO4

What procedure is this?

1. Place 1-mL of H2SO4 in test tube

2. Add 1-2 drops of the sample to their assigned test tube

3. Determine which sample is MISCIBLE or IMMISCIBLE

organic solvent

Hydrocarbon are soluble in ___________________

directly

the number of carbon is ______________ proportional to hydrophobicity

inversely

the number of carbon is ______________ proportional to polarity and water solubility

five

more than _____ carbon is insoluble in water

water (polar solvent)

As the percentage of HC in a given molecule increases:

a. _____________________ solubility decreases

b. _________________________ solubility increases

a = ?

ether (organic/non-polar solvent)

As the percentage of HC in a given molecule increases:

a. _____________________ solubility decreases

b. _________________________ solubility increases

b = ?

inversely

Solubility is ________________ related to melting point

cis-

in isomers, this configuration is the most soluble

inversely

solubility are ________________ proportional to molecular weight and IMF

branched-chain

is branched or straight-chain more soluble?

Ignition Test

Procedure:

1. Place 3-5 drops of sample in a small evaporating dish.

2. Light the sample with a match. Observe the results

3. Observe for sample’s: Flammability, Color of flame, and Burning time

Combustibility

measure of how easily a substance bursts into flame through fire or combustion

Complete Combustion

C_xH_y + O₂ —> CO₂ + H₂O

Incomplete Combustion

C_xH_y + O₂ —> CO₂ + CO + C + H₂O

soot

elemental carbon; black, carcinogenic substance that are formed due to insufficient oxygen in incomplete combustion

CO (Carbon Monoxide)

toxic, colorless, odorless gas that was produced during incomplete combustion

Flammability

ease with which a combustible substance can be ignited causing fire, combustion, or even explosion

indirectly

the carbon-hydrogen ratio, luminosity, and soot is ____________________ proportional to the efficiency of combustion

Baeyer’s Test, Bromine Test, and Iodine Test

tests of unsaturation for hydrocarbons

Baeyer’s Test

Procedure:

1. Place 5 drops of the sample in a clean and dry test tube.

2. Add 2 drops of 2% KMnO4. Observe for decolorization.

3. Observe as for the formation of brown sludge or suspension.

   • Use water as standard for decolorization

   • Decolorization immediately happens within a minute

2% KMnO4

solvent added to the hydrocarbon for Baeyer’s Test

brown sludge or suspension

what is formed when Baeyer’s Test is positive?

Bromine Test

Procedure:

1. Place 5 drops of the sample in a clean and dry test tube.

2. Add 10 drops of 0.5% Br2. in CCL4 reagent. Shake. Observe for Decolorization.

3. Observe as for the formation of bromine discharge (brownish red). In addition, place a moistened blue litmus paper on a glass rod and place it across the mouth of the test tube. Note the color change.

0.5% Br2 in CCl4 reagent

reagent used in the Bromine Test for unsaturation

brownish red

what is formed when Bromine Test is positive?

Baeyer’s test

• uses KMnO4

• form of oxidation reaction

• forms a brown suspension/sludge

• detects the presence of active unsaturation like in alkenes and alkynes

Bromine test

• uses Br2 in CCl4 to confirm the presence of double/triple bonds

• an electrophilic addition reaction through halogenation

• solution is decolorized when mixed with unsaturated compounds

Iodine test

• uses I2 solution

• electrophilic addition reaction through halogenation

• used to confirm the presence of alkene/alkynes

• positive result for this test is the formation of a tan-colored solid while retaining the color of the I2 solution.

Test for Aromaticity via Nitration Reaction

Procedure:

1. Place 5 drops of sample in a clean and dry test tube.

2. Add 8 drops of the nitrating mixture.

3. Shake vigorously for complete mixing. Observe for yellow oily layer or droplet

4. Dilute the resulting solution with 2 drops of water. Observe for reaction

5. If no observed reaction, place the test tube in a water bath for 10 mins.

6. Dilute with 20 drops of water. Observe results

Nitration

• common substitution reaction for aromatic molecules

• used to detect the presence of benzene rings in a compound

yellow oily layer

The formation of a _______________________ confirms the presence of a benzene ring.

electron-donating groups (e.g. - CH3)

The presence of _________________________ on the benzene ring will result into faster reaction.

Basic Oxidation

Procedure:

1. Place 4 drops of sample in a clean and dry test tube.

2. Add 8 drops of 2% KMnO4 and 3 drops of 10% NaOH. Place the test tubes in a water bath for 20 minutes.

3. Observe for color change or brown precipitate.

2% KMnO4 and 10% NaOH

reagent used in Basic Oxidation

brown precipitate

result of when Basic Oxidation is positive

Basic Oxidation

• uses KMnO4 in NaOH solution

• often referred to as mild oxidation

• can be used to detect the presence of alkene and benzylic carbon (must have benzylic hydrogen) that are both susceptible to oxidation

• brown precipitation or suspension confirm the presence of the target organic compounds