1. Introduction to Organic Chemistry [revised] Flashcards
- Chemistry of the compounds present in
living organisms. - They all contain carbon.
- Chemistry of carbon
organic chemistry
natural sources of organic compounds
Carbohydrates /
Proteins / Fats /
Vitamins /
Antibiotics
- all are obtained from living things
crude oil or coal undergoes into what process which results in alkanes/alkenes/alkynes/aromatic/hydrocarbon compounds?
Fractional distillation / destructive distillation
In the past, it is believed that _____ compounds are obtained from living organisms while ______ compounds are obtained from non-living sources.
organic compounds
inorganic compounds
In 1828, a German chemist produced _____, an organic compound (known to be excreted by mammals) by heating _________, an inorganic compound.
who is the German chemist?
urea
ammonium cyanate
Friedrich Wohler
Organic chemistry is the study of carbon compounds except for the SIX COMPOUNDS obtained from natural sources or synthesized in the laboratories.
what are the six compounds?
CO, CO2, carbonates, hydrogencarbonates, carbides and cyanides
ability of atoms in forming stable bonds into chains with itself, hence joining up or rings.
catenation
bond strength ____ as bond length ____
decreases
increases
bond strength ____ as the number of lone pairs ____
decreases
increases
SinH2n+2 n = 1 to 6 only →
silanes
GenH2n+2n = 1 to 3 only →
germanes
SnnH2n+2 : Only SnH4 (_____) exists
stannane
defined as an atom or a group of atoms that effectively determines the chemical properties of an organic compound
functional group
does not react with sodium
propane
- react with sodium to give hydrogen gas
- contain the same functional group–OH
- classified into the same homologous series: alcohols
Ethanol and propan-1-ol
a series of compounds that have the same functional group, and each member differs from the next member by a– CH2– unit in their formulae.
homologous series
Members in the same series can be represented by a
general formula
formula for alkane
CnH2n+2
formula for alkene
CnH2n
formula for alkyne
CnH2n-2
what is the mass of an electron
9.11 x 10 ^ -31 kg
9.11 x 10 ^ -28 g
the longer the carbon chain in the molecule (the greater the molecular mass):
➔ the ____ the attractive force between molecules
➔ the ____ the boiling point and density
greater
higher
Solubility depends on the _____ of organic molecules and the ______.
polarity and solvent
- Non-polar or weakly polar compounds dissolve readily in non-polar or weakly polar solvents.
- Highly polar compounds dissolve readily in highly polar solvents.
“like dissolves like”
solubility of hexane in tetrachloromethane
soluble
solubility of hexane in water
insoluble / immiscible
Molecules having ⎯OH or ⎯ NH2 groups are able to form
hydrogen bonds
affect the physical properties of alcohols and amines with low molecular masses
hydrogen bonds
Molecules with ____ groups are able to form hydrogen bonds with surrounding water molecules
➔Soluble in water
⎯OH
Molecules with higher molecular masses have ______ melting point, boiling points and density.
Higher molecular masses
➔ ____ molecular sizes
➔ ____ London dispersion forces among molecules
higher
large molecular sizes
stronger london dispersion forces
boiling point and density are lower compared to its straight-chain isomer
molecules with branched chains
_____ have greater surface area in contact with each other
➔Greater attractive force among the
molecules
Straight-chain isomers
melting point is higher compared to its straight-chain isomer
molecules with branched chains
Nowadays, scientists have discovered that many organic compounds can be synthesized from _____ substances.
inorganic
These compounds have been traditionally classified under inorganic chemistry.
carbon monoxide, carbon dioxide, carbonates, hydrogencarbonates, carbides and cyanides
bond enthalpy of C ⎯ C single bond is ___ kJ mol-1
356 kJ mol-1
______, unlike carbon, does not catenate to form diverse molecular structures.
silicon
element that has a much lower tendency to catenate than carbon.
sulphur
Name the homologous series of organic compounds that contain oxygen atoms in their functional groups.
Alcohol, ether, aldehyde, ketone, carboxylic acid, ester, acyl halide, amide and acid anhydride
Why is oil immiscible with water?
Oil molecules do not have free ⎯OH groups, so they cannot form hydrogen bonds with water molecules.
The relative molecular mass of glucose is 180.0, but it is soluble in water. Why?
Glucose molecules have ⎯OH groups, so they are able to form hydrogen bonds with water molecules. Therefore, glucose is soluble in water despite it has a high molecular mass.
Despite the fact that butan-1-ol and ethoxyethane have the same relative molecular mass, they have very different boiling points. The boiling points of butan-1-ol and ethoxyethane are 117C and 35C respectively. Explain the difference.
There is an ⎯OH group in butan-1-ol. Thus, butan-1-ol molecules are able to form hydrogen bonds with one another and the energy required to separate butan-1-ol molecules would be much greater.
Whereas for ethoxyethane, the attraction among the molecules is weak van der Waals’ forces only.
The amount of energy required to break the forces would not be great.
Therefore, the boiling point of ethoxyethane is lower than that of butan-1-ol.
Explain why propan-1-ol is soluble in water but 1-chloropropane is insoluble in water.
The ⎯ OH group of propan-1-ol molecules enables it to form hydrogen bonds with water molecules.
Thus it is soluble in water.
Although 1-chloropropane is a polar molecule, it does not form hydrogen bonds with water molecules. So it is insoluble in water.
Which molecule would have a higher boiling point, 1-bromobutane or 2-bromobutane? Why?
1-bromobutane would have a higher
boiling point.
1-bromobutane is a straight-chain molecule while 2-bromobutane is a branched-chain molecule.
Straight-chain molecules have a greater surface area in contact with each other, so greater intermolecular forces exist among the molecules.
Higher energy is required to break down the intermolecular forces among the molecules of 1-bromobutane.
1-Chlorobutane and 2-chloro-2-methylpropane have the same molecular mass, yet their melting points differ. The melting point of 1-chlorobutane is–123C while that of 2 chloro-2-methylpropane is–27.1C. Explain the difference
Melting point is a measure of how efficient the molecules are packed together in the solid state instead of just comparing the van der Waals’ forces among molecules.
Hence melting point is a function of the efficient packing of molecules but not the contact surface area.
1-Chlorobutane = straight-chain molecule
2-chloro-2-methylpropane = branched-chain molecule.
2-chloro-2-methylpropane = more spherical and symmetrical
(molecules are packed more efficiently in the solid state)
1-Chlorobutane = linear in shape and flattened
(packing in the solid state is not so efficient)
Hence, it has a lower melting point than 2-chloro-2-methylpropane.
What are the major factors that affect the physical properties of organic compounds?
- functional groups
- dipole moment of the molecule
- formation of hydrogen bonding between molecules
- length of carbon chains of the molecule.
The melting point and boiling point of pentane are–130C and 36.3C respectively while the melting point and boiling point of 2,2-dimethylpropane are–15.9C and 9.5C respectively. Account for the difference in melting point and boiling point between the two isomers.
Pentane = straight-chain molecule
2,2-dimethylpropane = branched-chain molecule
STRAIGHT CHAIN MOLECULES = have a
greater surface area in contact with each other than branched chain molecules. They are held together by stronger intermolecular forces.
Therefore, pentane has a higher boiling point than 2,2-dimethylpropane.
Molecules of 2,2 dimethylpropane = more spherical in shape (packed more efficiently in the solid state)
Molecules of pentane = linear in shape and flattened (packing in the solid state is not efficient)
Since extra energy is required to break down the efficient packing of 2,2-dimethylpropane, 2,2-dimethylpropane has a higher melting point than pentane
Which molecule, hexane or cyclohexane, would have a higher melting point? Explain your answer.
Cyclohexane > melting point than hexane.
Molecules of cyclohexane are more spherical in shape (packed more efficiently in the solid state)
Molecules of hexane are linear in shape and flattened (packing in the solid state is not efficient) S
Since extra energy is required to break down the efficient packing of cyclohexane, cyclohexane has a higher melting point than hexane.
Arrange the following molecules in increasing order of boiling points. Explain your answer.
Butane
Propanal
Propan-1-ol
butane < propanal < propan-1-ol
BUTANE = NON-POLAR.
Their molecules are held together by weak instantaneous dipole-induced dipole interactions.
A relatively small amount of energy is required to separate themolecules in the process of boiling.
propanal and propan-1-ol = polar molecules.
propanal = held together by relatively weak dipole-dipole interactions
propan-1-ol = held together by intermolecular hydrogen bonds.
Since the intermolecular forces present in molecules of propan-1-ol are stronger than those present in molecules of propanal, a larger amount of energy is required to separate the propan-1-ol molecules in the process of boiling.
