Polarity & Physical Properties

Question 1

What are the physical properties of cyclic hydrocarbons

Answer 1

• non-polar & have similar physical properties as their straight-chain counterparts
• insoluble in water, HOWEVER, cyclopropane is the exception
• the BP and MP of cyclic hydrocarbons is slightly higher than straight chain hydrocarbons with the same number of C atoms

Question 2

What are the physical properties of aldehydes?

Answer 2

• the carbonyl group (C=O) is very polar, but the carbon-hydrogen bands are NOT
• aldehydes cannot H bond with one another but they can H bond with water
  (the strength of attraction among aldehyde molecules is not as strong as that between alcohol molecules)
• their BP is lower than alcohols that have the same number of C atoms
• 3-14 C long are liquid at room temp;15 and more C are waxy solids
• 1-4 C are soluble in water; 5-7 C are slightly soluble in water (longer than 7 is insoluble)
• short chain aldehydes have a very pungent odour; as it gets longer, odour becomes more pleasant

Question 3

What are the physical properties of esters?

Answer 3

• > C=O groups make esters somewhat polar but without the -OH group, they CANNOT form hydrogen bonds with one another
• BP are lower than corresponding alcohols and carboxylic acids
• smaller esters are liquid at standard temp while longer chain esters are waxy solids
• 4 or fewer C atoms are soluble in water; large esters are insoluble
• most noticeable characteristics is their volatility, which allows them to generate aromas (SMELL THE BEST)

Question 4

What are the physical properties of carboxylic acids

Answer 4

• presence of >C=O group and the -OH group make the carboxyl group very polar, allowing carboxylic acids to H bond with one another
• the BP are much higher than other hydrocarbons with same number of C atoms
• short-chain are liquids at standard temps while longer chains are waxy solids
• polarity of carboxyl groups makes small carboxylic acids soluble in water (more than 10 C are insoluble)
• 1-4 C acids are completely miscible with water
• weak acids; conduct electric current

Question 5

What are the physical properties of alkanes

Answer 5

• non-polar, not soluble in water (soluble in benzene and other non-polar solvents)
• small alkanes are gases at standard temp; medium are liquid and large are waxy solids
• shape and size of the molecule affects boiling point
  ~ highly branched chain have less BP than straight chain molecules

Question 6

What are the physical properties of ketones

Answer 6

• ketones have a carbonyl group that is very polar but have NO hydrogen atoms bonded to strongly electronegative atoms
• CANNOT H-bond with one another but CAN H-bond with water molecules
• have BP and solubility similar to aldehydes
• carbon chains of 15 atoms or longer are waxy solids at room temp; smaller ketones are liquids

Question 7

What are the physical properties of aromatic compounds

Answer 7

• benzene is a liquid at standard temperature
• the BP of simple aromatic hydrocarbons are very similar to the aliphatic hydrocarbons with the same number of carbon atoms
• aromatic = strong odours

Question 8

What is the order of hydrocarbon derivatives of same size in terms of polarity (from greatest to least)?

Answer 8

amide > acid > alcohol > ketone = aldehyde > amine > ester > ether > alkane

Question 9

What are the physical properties of alkynes

Answer 9

• non-polar and insoluble in water
• first few alkynes exist as gases at standard temp
• have higher BP than corresponding alkanes
• linear structure of alkynes and nature of the triple bond causes them to attract one another more strongly than alkenes or alkanes
  (takes more energy to overcome these attractive forces)

Question 10

What are the physical properties of ethers

Answer 10

• bond angle formed by the C-O bonds make them slightly polar; if the bonds form a straight line, the two bond dipoles would cancel each other
• are not as polar as the other hydrocarbon derivatives
• CANNOT hydrogen bond with one another, making the attraction between them small
• can form H-bonds with water molecules
• ethers with 2-3 C atoms are soluble in water; straight chains with 4-6 C atoms are slightly soluble; all larger ones are insoluble
• 2-3 carbon ethers are gases at room temp; larger ethers are liquids

Question 11

What influences physical properties for organic chemicals. Explain briefly.

Answer 11

1. Size (mass) of molecule
   ~ higher mass= higher melting point/boiling point
   ~ london dispersion force
2. Shape of molecule
   ~ less branching = high MP/BP
3. Polarity of the molecule
   ~ more polar = higher MP/BP
   ~ dipole-dipole force or even hydrogen bonding

Question 12

What are the physical properties of amines

Answer 12

• the N-H bonds in primary and secondary amines are VERY polar; tertiary amines DO NOT have N-H bonds
• primary and secondary can H bond with themselves and with one another but tertiary cannot
• primary and secondary have high BP compared to ethers and alkanes of same size (higher BP then tertiary amines with same number of C atoms)
• ALL AMINES CAN H BOND; smaller amines are very soluble in water

Question 13

What are the physical properties of amides?

Answer 13

• Have a polar carbonyl group & primary and secondary amides have at least one -NH group
• can form STRONG H BONDS among themselves
• BP is much higher than other hydrocarbon derivatives of same size
• amides can form hydrogen bonds with water, making the small amides are very soluble in water

Question 14

What are the physical properties of alkenes

Answer 14

• more reactive than alkanes
• non-polar, not soluble in water (would separate instantly if dissolved) as attractive forces between alkene molecules are stronger than attractive forces between alkene molecules and water
• soluble in non-polar solvents
• first 3 alkenes are gases at standard temp and the rest are liquid
• BP of alkenes are slightly less than alkanes with the same number of C
• if there is more than 4 carbons, there is more than one possible position for the double bond; this affects boiling point (location of C=C)

Question 15

What are the physical properties of alcohols

Answer 15

• the hydroxyl (-OH) group is very polar, making small alcohols polar
• smallest alcohols are miscible (can be mixed in all proportions) with water
• as the hydrocarbon chain becomes longer, non-polar characteristics take over the polarity of the OH group, making the alcohol less soluble in water
• OH group allows H bonding
• BP of pure alcohols is much higher than corresponding alkanes
  ~ all straight chain alcohols with less than 12 C atoms are liquid at standard temp

ALL ALCOHOLS ARE TOXIC

Question 16

What are the physical properties of haloalkanes

Answer 16

• smallest haloalkanes (eg. fluoromethane, chloromethane) are slightly soluble in water; all other hydroalkanes are insoluble in water
• the BP of haloalkanes differ greatly from the BP of alkanes with the same number of carbon atoms