2.4 organic compounds Flashcards
how do you name a halogenalkane?
-F = fluoro-
-Cl = chloro-
-Br = bromo-
-I = iodo-
how do you name an alcohol/hydroxyl? -OH
-OH = -ol or hydroxyl-
e.g ethanol
how do you name a carboxylic acid? -COOH
-COOH = -oic acid
e.g ethanoic acid
how do you name an alkene? C=C
C=C = -ene
how do you name an aldehyde? -CHO
-CHO = -al
e.g ethanal
how do you name a ketone? -CO
-CO = -one
e.g propaneone
how do you name an ester? -COO
-COO = -oate
what are the rules to naming compounds?
- find longest carbon chain
- identify the functional groups
- number the carbon atoms in the chain so that the functional group has the lowest possible number
- the prefixes are listed in alphabetical order
- if there’s more than one identical side chain or functional group, use di-, tri-, tetra-
- commas are put between numbers and dashes are put between numbers and letters
- a cyclic (ring) hydrocarbon is designated by the prefix cyclo-
what is the empirical formula?
the simplest whole number ratio of atoms of each element in a compound
what is the molecular formula?
the actual number of atoms of each element in a molecule
(this doesn’t show the functional group of a compound)
what is the displayed formula?
shows all the arrangement of atoms, and the bonds linking them in the compound
this clearly shows the functional group present and would be used when considering a reaction mechanism
what is the shortened formula?
shows the atoms carbon by carbon as well as the attached hydrogens and functional groups so that the structure is unambiguous
it cannot be used if details of the bonds are needed
what is the skeletal formula?
only shows the bonds of the carbon skeleton as well as any functional groups
it can reduce confusion when complex molecules are being considered and is widely used in research
what are structural isomers?
compounds with the same molecular formula but different structural formula
what are the 3 different types of structural isomerism we need to know about?
- chain isomerism
- position isomerism
- functional group isomerism
what is chain isomerism?
when the carbon chain of the molecule is arranged differently
what is positional isomerism?
when the side or position of the functional group differs
what is functional group isomerism?
when the functional group in the compounds is different
to boil a liquid (or melt a solid), energy (generally in the form of heat) is needed to overcome the forces that hold the particles together in that solid or liquid
what forces do hydrocarbons have between their molecules?
only induced dipole-induced dipole or van der Waals forces
so their intermolecular forces are very weak
why, as the chain length of a hydrocarbon gets longer, does the boiling point increase?
- van der waals forces act between the surfaces of the molecules
- the more surface there is in contact, the stronger the forces
- as the chain length gets longer, the surface contact between the molecules gets bigger
- as a result it takes more energy to overcome the van der Waals forces and the boiling and melting temperatures increase
small hydrocarbons are (solid/gases/liquid) at room temperature?
gases
large hydrocarbons are (solid/gases/liquid) at room temperature?
liquids
the largest hydrocarbons are (solid/gases/liquid) at room temperature?
solid
a branched-chain alkane has a (lower/higher) boiling point than its straight-chain isomer?
lower
why do branched-chain alkanes have a lower boiling point than their straight-chain isomers?
branched-chain alkanes can’t pack closely together so they have smaller molecular surface areas
- the more branches an isomer has, the less surface contact there is between molecules
- less surface contact means weaker VdW forces between molecules and so less energy is needed to separate them, resulting in lower boiling temperatures
when looking at boiling and melting temperatures of organic compounds other than hydrocarbons, what do we need to consider?
all other possible intermolecular forces
list butane, chloroethane and propan-1-ol in order of lowest to highest boiling temperature
butane = 0.C
chloroethane = 12.C
propan-1-ol = 97.C
why does e.g butane have a low melting/boiling temperature?
the only intermolecular forces it has are induced dipole-induced dipole forces
why does chloroethane have a medium boiling temperature?
- has polar C-Cl which give rise to a permanent dipole
- therefore, there are extra dipole-dipole forces between the molecules and more energy is needed to break those bonds
why does e.g propan-1-ol have a high melting/boiling temperature?
- in propan-1-ol, hydrogen bonds occur between the -OH groups
- since hydrogen bonds are the strongest intermolecular forces, even more energy is needed to break them, resulting in the largest boiling temperature
what do we need to know when considering the solubility of an organic compound in water?
what type of intermolecular interactions form between the compound and water molecules
what will organic compounds that can form hydrogen bonds with water do in water? why?
will dissolve
since hydrogen bonds are the most significant intermolecular forces between water molecules
what will compounds like butane and chloroethane do in water? why?
they won’t dissolve
because they only form induced dipole-induced dipole or dipole-dipole forces between molecules and are not able to form significant attractions with the water molecules
what will alcohols and carboxylic acids do in water? why?
- -OH groups can form hydrogen bonds with water
- however solubility decreases as chain length increases, so only the smaller alcohols and carboxylic acids are soluble
- the larger alcohols and carboxylic acids have longer hydrocarbon chains which are hydrophobic. at about four of rive carbons, the hydrophobic effect is so large that the compound is no longer soluble
for alcohols and carboxylic acids, solubility decreases as chain length ____?
increases
explain why ethanoic acid is soluble in water but hexanoic acid is not
- ethanoic acid is soluble bc it can form hydrogen bonds with the water
- in hexanoic acid, although the -COOH group forms hydrogen bonds with water, the longer carbon chain cannot form hydrogen bonds. this exerts such a large hydrophobic effect that the compound is insoluble
(in hezan-1-ol the carbon chain is longer so the effect of the -OH group is now small (so is insoluble)
what is an electrophile?
an electron-deficient species that can accept a lone pair of electrons
most electrophiles are positively charged or have an atom that carries a partial positive charge e.g H+, NO2 + and H δ+ - Br δ-
what is a nucleophile?
a species with a lone pair of electrons that they can donated to an electron-deficient species
- many nucleophiles are negatively charged, formed by gaining electrons
- they are electron-pair donors
-e.g OH- , CN- and NH3 - attacks regions of low electron density
what is a free radical?
a species with an unpaired electron
- the unpaired electron is shown by a dot on the species
e.g Cl• and •CH3
are radicals highly reactive? why?
yes
radicals are highly reactive as a result of the unpaired electron
what is bond fission?
- a single covalent bond is a shared pair of electrons between two atoms
- breaking a covalent bind is called bond fission
what are the two ways bond fission can happen?
- homolytic fission
- heterolytic fission
what is homolytic fission?
- where the bond breaks equally, and each of the bonded atoms receives one of the electrons from the bonded pair
- two free radicals are formed
e.g C2H5Cl -> C2H5• + Cl•
what is formed by homolytic fission?
2 radicals
what is the general formula for homolytic fission?
XY -> X• + Y•
what is heterolytic fission?
- where the bond breaks unequally with one of the bonded atoms receiving BOTH electrons from the bonded pair
- a positively charged ion (cation) and a negatively charged ion (anion) are formed (one nucleophile and one electrophile)
e.g CH3CH2Br -> CH3CH2 + + Br -
what is formed by heterolytic fission?
- a positively charged ion (cation) and a negatively charged ion (anion) are formed
(one nucleophile and one electrophile)
what is the general equation for heterolytic fission?
XY -> X+ + Y-
each carbon can make how many bonds?
4 bonds
each hydrogen can make how many bonds?
1 bond
each oxygen can make how many bonds?
2 bonds
each nitrogen can make how many bonds?
3 bonds
each halogen can make how many bonds?
1 bond
is
. H H
I I
-C-C-OH
I I
H H
a displayed formula?
no - all of the bonds must be shown
so the bond between the O-H must be shown
what is the longest carbon chain called?
the parent chain
what is the order or precedence/importance of functional groups?
- carboxylic acid (most important)
- aldehydes
- ketones
- alcohols
- alkenes (least important)
is CH2(OH)2 a molecular formula?
no - it should be CH4O2
in alkenes, is the principle chain always the longest?
not always
it must contain the double bond
(put probably is still longest)
prefix of e.g dimethyl but for:
3
4
5
6
1 = methyl
2 = dimethyl
3 = tri
4 = tetra
5 = penta
6 = hexa
how do you name a compound with two alcohol groups? (e.g one on each end with 2 carbons?)
ethane-1,2-diol
why does it mean that carboxylic acid is high on the priority list?
the numbering of the carbon chain starts on the C that is part of the -COOH group
what does the letter R mean in a molecule?
it means that part of the molecule’s structure is unknown or too big to draw
- so you can’t name these compounds unless additional info is given where you could work it out
what is a hydrocarbon?
a compound of carbon and hydrogen only
what is a saturated compound?
one that contains no C=C double bonds
what is an unsaturated compound?
one which contains C=C double bonds
alkanes are (saturated/unsaturated) hydrocarbons?
saturated
what is the general formula of alkanes?
CnH2n+2
in what does E/Z isomerism occur? why?
- in alkenes (and substituted alkenes)
- due to restricted rotation about the double bond
what does the single bond in alkanes allow?
free rotation
what does the double bond in alkenes mean?
that rotation is restricted
how do you name E/Z isomers?
- look at the nature of the atom directly attached to each of the carbon atoms in the double bond
- the atom with the higher atomic number takes precedence
- if they are both on the same side of the double bond, it is the Z isomer, and if they are on opposite sides, it is the E isomer
is it an E or Z isomer if both of the higher priority groups are on the same side of the double bond?
Z isomer
can E/Z isomers have different physical and chemical properties?
yes
since the functional groups are held differently
what is a homologous series?
a series of organic compounds with the same functional group where each successive member differs by CH2
(the compounds have the same general formula)
what is a functional group?
an atom or group of atoms responsible for the characteristic reactions of that compound
what is the general formula of a carboxylic acid?
CnH2n+1COOH
how does the chain length affect the melting/boiling point of an organic compound?
the longer the chain length, the higher the melting/boiling point
this is because the longer the carbon chain, the more points of contact there are between molecules. this means there are stronger temporary dipoles between molecules so more energy is required to overcome the intermolecular forces
how does the chain length affect the solubility of an alcohol?
as chain length increases, alcohols become less soluble in water
in water, the alcohol OH group forms a hydrogen bond with water which replaces hydrogen bonds between water molecules. only the OH group in alcohols can form H bonds, so longer alcohols disrupt the hydrogen bonding between water molecules but dont replace them with additional H bonds, as the CH2 groups dont form these bonds
why are alcohols and carboxylic acids soluble in water?
they can form hydrogen bonds with water molecules and therefore they are soluble in water
compare the boiling points of alcohols, alkanes and carboxylic acids:
alkanes < alcohols < carboxylic acids
- bc alkanes - only temporary dipole forces between molecules, which are relatively easy overcome
- alcohols and carboxylic acids both form hydrogen bonds which require a lot of energy to overcome and therefore they have the higher boiling points
- carboxylic acids have the highest boiling points because two possible hydrogen bonds can be formed per carboxylic acid molecule
why can’t:
.H3C H
\ /
C=C
/ \
H3C H
exist as an E-Z isomer?
- because (one of) the double bonded carbon atoms has two groups attached to it which are the same
it can only be an e-z isomer if each of the double bonded carbon atoms have two different groups attached to it
