S3.2 - functional groups: classification of organic compounds Flashcards
What is empirical formula?
Empirical formula is the simplest whole number ratio of atoms in a compound.
What is molecular formula?
Molecular formula is the actual number of atoms in a molecule.
M = (molar mass of empirical formula)n
What is structural formula?
Structural formula is a representation of the molecule, showing how atoms are bonded to each other.
What are the 3 types of structural formula?
- Full structural formula
- Condensed structural formula
- Stereochemical formula
What is a full structural formula?
- Shows every bond and atom
- Uses 60, 90 and 180 which is clear, but isn’t the true geometry.
What is a condensed structural formula?
Groups atoms together and emits assumed C-H bonds to minimize formula.
CH3CH3
What is stereochemical formula?
3D model that shows the position of atoms and groups around a central atom.
What are limitations of the molecular formula?
Properties of a compound are determined not only by the atoms it contains, but how they are arranged relative to each other and space.
What is skeletal formula?
Shorthand representation of the structural formula, showing all bonds and symbols except C-H bonds.
- C-C bonds are represented by offset lines and position.
- Number of carbon atoms are identified by the vertices where the bond lines meet.
How can you find the number of hydrogen atoms attached?
Subtract the number of bonds drawn to the atom from 4.
What are aromatic compounds?
Molecules with a benzene ring (C6H6)
What is R?
Any alkyl (C2H6), with a general formula of (CnH2n+1)
What is unique about carbon and enables it to form more compounds than the sum of compounds formed by all the other elements?
Carbon atoms are able to sp, sp2 or sp3 hybridize.
- This allows carbon to form a variety of different compounds containing single, double or triple bonds.
What is catenation?
Carbon has a unique ability to link to itself and form chains of bonded carbon atoms, as well as ring structures such as benzene.
What are functional groups?
Atoms or groups of atoms that are present in organic compounds that are responsible for a compounds physical properties and chemical reactivities.
What does saturated and unsaturated mean?
Saturated - only contains single bonds.
Unsaturated - contains double or single bonds.
What is a reaction pathway?
Each step in a reaction involves a similar reactant from a previous product and involves a functional group inter-conversion in a series of discrete steps.
What makes up an amino acid?
- Amine group (NH3)
- Carboxylic acid group (COOH)
- R group
- Hydrogen
What happens during a condensation reaction between amino acids?
Water is lost and a new bond is formed between the acid group of 1 amino acid and the amino group of another (peptide bond).
What is the general formula, suffix name and name of functional group of alkanes?
What is the general formula, suffix name and name of functional group of alkenes?
What is the general formula, suffix name and name of functional group of alkynes?
What is the general formula, suffix name and name of functional group of alcohols?
What is the general formula, suffix name and name of functional group of ethers?
What is the general formula, suffix name and name of functional group of aldehydes?
What is the general formula, suffix name and name of functional group of ketones?
What is the general formula, suffix name and name of functional group of carboxylic acids?
What is the general formula, suffix name and name of functional group of esters?
What is the general formula, suffix name and name of functional group of amides?
What is the general formula, suffix name and name of functional group of amines?
What is the general formula, suffix name and name of functional group of halogeneoalkanes?
What is the general formula, suffix name and name of functional group of arenes?
What do functional groups influences?
What is a homologous series?
Family of compounds in which each successive member differs by CH2 and can be described by a general formula.
What are trends in boiling points of homologous series?
Boiling points increase with increasing carbon number due to increased IMF as molecular size increases.
Which IMF is affected?
LDF’s increase in strength.
How can functional groups affect volatility?
Most –> least volatile:
Alkane / Alkene / Alkyne / Halogeneoalkane / Aldehyde / Ether / Ester / Ketone / Alcohol / Amine / Amide / Carboxylic acid
How can functional groups affect the type of IMF present?
LDF –> Dipole-Dipole –> Hydrogen bonding
Alkane / Alkene / Alkyne / Halogeneoalkane / Aldehyde / Ether / Ester / Ketone / Alcohol / Amine / Amide / Carboxylic acid
What do successive homologous series differ by?
CH2
What is the IUPAC nomenclature?
set of rules used by the International Union of Applied Chemistry to apply systematic names to organic and inorganic compounds
What are the steps in naming compounds?
- Identify the stem - longest straight chain of carbon
- Identify the functional group - determines the suffix (ane for alkanes)
- Identify side chains - determines the prefix (methyl for CH3)
How are esters formed?
Alkyl group of an alcohol replaces the hydrogen in a carboxylic acid in a condensation reaction
How are ethers formed?
Two alkyl groups joined by an oxygen atom
How do you name ethers?
Longer chain forms the stem and retains the alkane name (propane) and shorter chains is given the prefix alkoxy (methoxy for 1 carbon)
How do you name esters?
Salts take the stem of the name (ethyl) and the alcohol forms the suffix (propanoate)
What are the 3 possible parts of IUPAC nomenclature?
- Prefix - position, number and name of substituents
- Stem - number of carbon atoms in the longest chain
- Suffix - class of compound determined by functional group
What are structural isomers?
molecules that have the same molecular formula but different arrangements of the atoms so have different chemical and physical properties
What are the properties of branched structural isomers?
the more branching present, the lower the melting point due to reduced surface contact which weakens the strength of the LDF’s between neighboring molecules (instantaneous and induced dipoles)
What are the 4 types of structural isomers?
- branched
- unbranched
- positional
- functional group
How are branched structural isomers used within the industry?
branched chain isomers burn more smoothly in internal combustion engines
- factions with more branched chains are premium - higher octane number
What are positional structural isomers?
isomers with the same molecular formula and functional group, but in a different position
What are functional group structural isomers?
isomers with the same molecular formula but a different functional group
What are primary compounds?
the C attached to the OH group is attached to 1 other C atom
What are secondary compounds?
the C attached to the OH group is attached to 2 other C atoms
What are tertiary compounds?
the C attached to the OH group is attached to 3 other C atoms
Why are numbers assigned to ring positions of the substituted benzene?
So that the lowest numbers possible are obtained.
When are substituted benzene compounds formed?
Formed when H molecules in a Benzene atom are replaced by a halogen group or a functional group, including amino (NH2) or nitro (NO2).
Why are there no structural isomers for monosubstituted benzene?
All 6 positions in the hexagonal carbon ring are identical.
- However, 3 structural isomers for bisubstituted benzene does exist.
What does there being 3 disubstituted benzene structural isomers show?
Provides additional support for the accepted model of Benzene where it exists as a hexagonal ring with delocalised pi bonds and all C-C bonds having equal length.
What are stereoisomers?
What is isomerism?
What is a structural isomerism?
What is stereoisomerism?
What are the 2 types of stereoisomerism?
What is configurational isomerism?
What is conformational isomerism?
What are the 2 types of configurational isomerism?
What is cis-trans and isomerism?
What is optical isomerism?
Why can conformational isomers not be isolated seperately?
What molecules can cis-trans isomers occur with?
Why can isomers rise from double-bonded molecules?
Why can isomers rise from cyclic molecules?
What is a chiral?
What are alternate names for a chiral?
What are enantiomers?
What does non-superimposable mean?
What are diastereomers?
What is a polarizer?
What is plane-polarized light?
What is a polarimeter?
What is an analyser?
What does it mean to be optically active?
What is a racemic mixture?
What does it mean to be optically inactive?
How do 2 enantiomers of a chiral compound rotate?
What is asymmetric synthesis?
What are 3 types of analysis?
- Qualitative analysis
- Quantitative analysis
- Structural analysis
What is qualitative analysis?
Detection for the presence, not the quantity of a substance in a mixture.
What is quantitative analysis?
Measurement of the quantity of a particular substance in a mixture.
What is structural analysis?
Description on how atoms are arranged in molecular structures.
What are 3 common instrumental methods of analysis?
- Mass spectrometry
- Infrared spectroscopy
- Nuclear magnetic resonance spectroscopy
What is mass spectrometry used for?
Used to determine the relative atomic mass and molecular mass; the fragmentation pattern can be used as a fingerprint technique to identify unknown substances or for evidence of the arrangements of atoms in a molecule.
What does MS cause?
MS of organic compounds can cause fragmentation of the molecules.
What happens during mass spectrometry?
A parent ion breaks down into smaller ions to create a fragmentation pattern which provides useful information about the mass of individual atoms (RAM) and the abundance of relative isotopes.
How do you work out the molecular ion using a mass spectra?
Peak furthest to the right.
When is a molecular ion formed?
The molecular ion, or parent ion is formed when a molecule loses 1 electron, but otherwise remains unchanged.
What are the charges of peaks in a mass spectra?
Have to be +, otherwise they would not be detected.
What happens to radicals in MS?
Radicals aren’t +, so are not detected by MS and disappear into the atmosphere.
What is infrared spectroscopy?
Used to identify the type of bond present in a molecule.
What are the relative numbers like for IR in terms of energy, wavelength and frequency?
Frequency - large
Energy and wavelength - small
What can be identified from IR spectra?
It can identify the type of bond present in a molecule which can be determined by wavenumber and frequency.
What is wavelength?
The distance between 2 successive crests or troughs.
What is frequency?
Number of waves passing a point per second.
How do you calculate wave speed?
Wave speed = frequency x wavelength
What is wavenumber?
Measure of frequency commonly used in IR spectroscopy (cm-1).
- Number of peaks that occur in 1cm.
How do you work out the frequency of a wave in terms of wavenumber (cm-1)?
Frequency (cm-1) = 1 / wavelength (cm)
What are ER waves?
Electromagnetic waves that transfer energy and carry information by interacting substances in a different way.
How do radio waves interact with molecules?
Radio waves can be absorbed by certain nuclei, causing them to reverse their nuclear spin, telling us about the hydrogen environments in a molecule.
How do micro waves interact with molecules?
Micro waves cause molecules to increase their rotational energy and tell us about their bond lengths.
How does infrared radiation interact with molecules?
IR radiation is absorbed by bonds and causes them to stretch or bend in a specific way that tells us about the bond.
How does visible light and UV interact with molecules?
UV and visible light produces electronic transitions and tell us about energy levels in an atom.
How do x-rays interact with molecules?
X-rays have a wavelength similar to bond lengths in crystals which can be used to determine the crystal structure.
What does the natural frequency of a chemical bond depend on?
- Bond strength
- Masses of atoms
What happens when molecules absorb IR?
Absorbing IR excites the bonds in molecules.
- The energy needed to excite the bonds in a molecule occurs in the IR region.
When will a bond interact with IR?
A bond in a diatomic molecule will only interact with IR if it is polar as only polar bonds will absorb IR as the presence of partial - and + charges allows the electric field component of the EM to excite the vibrational energy of the molecule.
Which bonds are most common and why?
C-O / C–O / O-H / C-H
- These bonds absorb IR strongly
When will a bond in a diatomic molecule react?
If it is polar, it will react with the electric field and absorb IR.
What does a change in vibrational energy produce?
Changes in vibrational energy produces a corresponding change in the dipole moment in a molecule.
What does intensity of absorption depend on?
Polarity of the bond.
Why do symmetrical non-polar bonds in N—N and O–O no absorb radiation?
They do not interact with the electrical field.
What is the difference between a simple or complex molecule when they vibrate?
Simple molecule - bond stretches
Complex molecule - bond stretches and bends
What are the 3 fundamental frequencies of polyatomic atoms (water) ?
- Symmetric stretch ( same direction)
- Asymmetric stretch ( opposite direction)
- Symmetric bond
What are the 4 modes of vibration of symmetric linear molecules (CO2)?
- Inactive IR stretch (no change in dipole as molecule remains symmetrical)
- Asymmetric stretch (temporary dipole)
- 2 symmetric bonds (into/out of the plane of the page and is a temporary dipole).
What is a fingerprint region?
Region that can be used to identify an unknown compound.
What is the order of regions from high to low wavenumber?
1) C-H / O-H / N-H (single bond to H stretches)
2) C—C / C—N (triple bond stretches)
3) C–C / C–O ( double bond stretches)
4) Fingerprint region
What are examples of short-wave radiation?
UV and visible light
What are examples of long-wave radiation?
IR
What is the global warming potential?
Compares the amount of IR energy absorbed by a gas compared to 1 tonne of CO2 over a period of time.
What is the greenhouse effect?
Short-wave radiation is absorbed by the Earth’s surface and emitted as long-wave radiation, which is absorbed by greenhouse gases and re-emitted back into the atmosphere, keeping the Earth warm.
What does the global warming potential depend on?
- How effective the individual gas atoms are at absorbing IR
- Atmosphere lifetime of a gas
How do you work out the structure of a compound?
- Look at IR spectra graphs.
- Identify peaks and waveneumber.
3 Use data booklet to work out which bonds are present.
What is proton nuclear magnetic resonance spectroscopy (HNMR)?
Used to show the chemical environment of Hydrogen atoms in a molecule, giving structural information about a molecule.
What is MRI?
Uses NMR in the presence of a powerful magnet where radio waves are used to generate electrical signals which produce either 2D or 3D images.
What is nuclear magnetic resonance spectroscopy?
Used to find the structure and shape of a molecule by identifying different protons in a molecule which are bonded to different atoms.
What 4 things can be deduced from NMR?
- Number of peaks in the spectrum
- Position or chemical shift of each peak
- Size or integrated area of each peak
- Splitting pattern observed for each peak
How does HNMR show the different chemical environments?
Number of peaks observed in a spectrum = number of different chemical environments
What is a chemical shift?
Position where a signal appears in a NMR spectrum ,measured in ppm
What is the link between chemical shifts and the position of the H atoms in a molecule?
The closer the atoms are to the OH group, the higher the chemical shift observed as the high electronegativity of O pulls electrons away from H, so nuclei become deshielded and more susceptible to the effects of the external magnetic field
What does the area under the curve depend on?
Number of nuclei in a chemical environment
What is an integrated trace?
Shows the relative number of H atoms in a chemical environment
How can we determine the number of peaks caused by splitting?
n+1, where n is the number of neighboring H atoms
How is the intensity of peaks determined?
Following Pascall’s triangle
What else should we consider when analyzing NMR?
- Protons bonded to the same atom do not interact with each other as they are equivalent and act as a group.
- Protons on carbon atoms that are not next to each other do not interact with each other as the magnetic fields are too far apart to interact with spin-spin coupling
- OH atoms don’t undergo spin-spin coupling with H of neighbor atoms as it isn’t split by other atoms.
