Introduction to Organic Chemistry Flashcards
What is organic chemistry
Chemistry of compounds present in living organisms
All organic compounds contain
carbon
Natural sources of organic compounds
Living things:
Carbohydrates
Lipids
Proteins
Nucleic acid
Year when Friedrich Wohler created urea from ammonium cyanate
1828
Who made urea out of ammonium cyanate
Friedrich Wohler
Organic chemistry was redefined as the study of compounds except:
CO2
CO
Carbonate
Hydrogencarbonate
Carbonite
Cyanide
Unique nature of Carbon
Ability to form strong covalent bonds
Electronic configuration of carbon
Ability to catenate
Ability to form multiple bonds
Electron configuration of carbon
1s22s23p2
Each carbon atoms has how many unpaired electrons when excited?
4
Carbon atoms link together to form chain of varying lengths, branched chains and rings of different sizes
Ability to catenate
The ability of atoms in forming stable bonds with itself, hence joining up
into chains or rings.
catenation
lower bond strength as bond length _____
increases
C-C > Si-Si > Ge - Ge > Sn - Sn
bond strength decreases as bond length increases
Bond strength decreases when the number of lone pairs ______
increases
An atom or a group of atoms that effectively determines the chemical properties of an organic compoun
Functional group
A series of compounds that have the same functional group, and each number differs from most members by a CH2 unit
Homologous compounds
Examples of Homologous compounds
Ketones
Aldehydes
Alcohol
Acid Anhydride
Amine
Members of the same series that can be represented by a general function
Homologous series
Ethanol and propan-1-ol reacts with sodium to give ___________
hydrogen gas
How does Ethanol and Propan-1-ol have similar chemical properties?
➔they contain the same functional group –OH
➔they are classified into the same homologous
series — alcohols
True or false: Members in the same series can be represented by a general formula.
true
True or false: Not all members of homologous series have similar chemical properties
False, Members of a homologous series
have similar chemical properties
Relationship between the length of the carbon chain to mass
directly proportional
Relationship between the length of carbon chain to attractive force
Directly proportional
Relationship between the length of carbon chain to melting point, boiling point, and density
Directly proportional
Main factors affecting the physical properties of organic compounds
Structure of the functional group
length of carbon chains
What is part of the structure of the functional groups
Dipole moment of the molecule
Formation of hydrogen bonds
Effects of carbon chains in physical properties of organic compounds
London dispersion forces
Molecules having a polar functional group have _______
a higher boiling point
Molecules having a polar functional group has _________
Stronger intermolecular attraction among molecules
Tetrachloromethane has ___________ in the
molecule.
4 polar bonds
Why does tetrachloromethane have low melting point and boiling point?
The molecule is non-polar since although the is a difference of electronegativity between the 4, since it is tetrahedrally symmetrical, the dipole moments cancel each other out.
Solubility of organic molecules depends on _______
the polarity of organic molecules and the solvent
______________- dissolve readily in non-polar or weakly polar solvents
Non-polar or weakly polar compounds
True or false: “Like dissolves like”
true
Why does Hexane dissolve readily in tetrachloromethane
The intermolecular forces among hexane and those tetrachloromethane molecules are equal to the intermolecular forces between hexane and tetrachloromethane molecules
Why is Hexane Insoluble in Water?
The forces between water is strong intermolecular forces, while weak intermolecular forces exist in hexane and water molecules
Molecules having ________ groups are
able to form hydrogen bonds
⎯OH or ⎯ NH2
Hydrogen bonds affect the physical properties of alcohols and amines with ________
low molecular masses
Why does Propan-1-ol have a Higher Boiling Point?
The stronger forces between molecules means that more energy is required to break apart the molecules
Formation of hydrogen molecules also affect the __________ of a molecule
solubility
Molecules with __________ are able to form hydrogen bond with surrounding water molecules, making it soluble in water
-OH groups
Molecules with higher molecular mass have higher _________
Melting point, Boiling point, and density
Higher molecular mass is indicative of ___________
Large molecule size
Stronger London dispersion forces among molecules
true or false: branched chain typically have higher melting points compared to straight-chain isomers
False
Why are straight chain isomers have lower density and boiling point
Straight-chain isomers have greater surface
area in contact with each other
➔ Greater attractive force among the
molecules
Why are branched chain isomers have higher density and boiling point
Branched-chain isomers are more spherical
➔ Packed more efficiently in solid state
➔ Extra energy is needed to break down the
efficient packing
How was organic chemistry defined before 1800s?
The knowledge of organic and inorganic
compounds was raised during the 1780s.
Scientists defined organic chemistry as the
study of compounds that could be obtained
from living organisms. They believed that the
synthesis of organic compounds took place in
living organisms only.
How is organic chemistry defined nowadays?
Nowadays, scientists have discovered that
many organic compounds can be synthesized
from inorganic substances. The updated
definition of organic chemistry is the study of
carbon compounds, except for carbon
monoxide, carbon dioxide, carbonates,
hydrogen carbonates, carbides and cyanides.
These compounds have been traditionally
classified under inorganic chemistry.
Why is carbon able to catenate?
The ability to catenate of carbon is chiefly due to the high strength of the C⎯C single bond (bond enthalpy of C ⎯ C single bond is 356 kJ mol-1).
Would you expect silicon, which is just below carbon in the
Periodic Table, to catenate to form diverse molecular
structures? Explain your answer.
Silicon, unlike carbon, does not catenate to form diverse
molecular structures. Carbon is able to catenate because
carbon atoms have a relatively small atomic size. This
enables a carbon atom to form strong covalent bonds
with other carbon atoms. However, due to the greater
atomic size of silicon, its ability to catenate is much lower
than that of carbon.
Would you expect sulfur, which has an
electronegativity value very close to carbon, to catenate? Why?
The electronic configuration of sulphur is 1s22s22p63s23p4
. It
has only two unpaired electrons. Its atomic size is larger than
that of carbon. So it has a much lower tendency to catenate
than carbon.
Name the homologous series of organic compounds
that contain oxygen atoms in their functional groups.
Alcohol, ether, aldehyde, ketone, Answer
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 117oC and 35oC 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 –123oC while that of 2-
chloro-2-methylpropane is –27.1 oC. 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 is a straight-chain molecule while
2-chloro-2-methylpropane is a branched-chain molecule. As
2-chloro-2-methylpropane is more spherical and symmetrical, its
molecules are packed more efficiently in the solid state.
1-Chlorobutane is linear in shape and flattened, its 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?
the structure of the functional groups, dipole moment of the
molecule, the formation of hydrogen bonding between molecules,
and the length of carbon chains of the molecule.
The melting point and boiling point of pentane are
–130oC and 36.3
oC respectively while the melting point
and boiling point of 2,2-dimethylpropane are –15.9
oC
and 9.5
oC respectively. Account for the difference in
melting point and boiling point between the two
isomers.
Pentane is a straight-chain molecule, while 2,2-dimethylpropane is
a branched-chain molecule. Straight-chain molecules have a
greater surface area in contact with each other than branched-
chain molecules. Straight-chain molecules are held together by
stronger intermolecular forces. Therefore, pentane has a higher
boiling point than 2,2-dimethylpropane. Molecules of 2,2-
dimethylpropane are more spherical in shape and are packed
more efficiently in the solid state. Molecules of pentane are linear
in shape and flattened, so their 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 has a higher melting point than hexane. Molecules
of cyclohexane are more spherical in shape and are packed more
efficiently in the solid state. Molecules of hexane are linear in
shape and flattened, so their packing in the solid state is not
efficient. Since extra energy is required to break down the efficient
packing of cyclohexane, cyclohexane has a higher melting point
than hexane.
