Functional Groups: Classification of Organic Compounds (DP IB Chemistry)

The condensed structural formula of propane is CH₃CH₂CH₃.

The skeletal formula of propene is:

False.

The stereochemical formula of 1-chloroethan-1-ol is:

False.

The structural formula of a chemical has all of the chemical bonds displayed, which means that ethanol is:

Functional groups are atoms or groups of atoms that are found in organic compounds and give them their characteristic physical and chemical properties.

True.

Organic compounds with the same functional group belong to the same class.

The functional group of an alkene is the carbon-carbon double bond (C=C).

The functional group for a carboxylic acid is -COOH.

True.

The IUPAC suffix for a ketone is -one.

For an amine:

• Functional group = -NH₂

• IUPAC prefix = amino-

• IUPAC suffix = -amine

Phenyl is the functional group name for aromatic compounds, implying that a benzene ring is present.

For an alcohol:

• Functional group = -OH

• IUPAC prefix = hydroxy-

• IUPAC suffix = -ol

True.

The functional group formula for an ester is R-COO-R.

The carbonyl functional group (C=O) is present in aldehydes and ketones.

True.

The functional group formula for an alkoxy compound is R-O-R.

The suffix for carboxylic acids is -oic acid.

Amides / amido compounds contain the following functional group.

A homologous series is a series or family of organic compounds that have similar features and chemical properties due to having the same functional group.

True.

A functional group is a group of atoms bonded in a specific arrangement that influences the properties of the homologous series

All members of a homologous series have:

• The same general formula

• Same functional group

• Similar chemical properties

• A clear trend in their physical properties

• The difference in the molecular formula between one member and the next is CH₂

The homologous series of alkanes contains only carbon-hydrogen bonds and saturated carbon-carbon bonds.

False.

The alkene functional group is represented by C=C.

The general formula for alkanes is C_nH_2n+2.

The general formula for alkenes is C_nH_2n.

The homologous series of alcohols has the general formula C_nH_2n+1OH.

False.

The general formula of the carboxylic acids is C_nH_2n+1COOH.

The general formula of an aldehyde is C_nH_2n+1CHO.

False.

Each homologous series can be described by a general formula.

False.

As the number of carbons in a straight-chain molecule increases, the boiling point increases.

In a homologous series, boiling point increases with molecular size due to the increased strength of London dispersion forces.

True.

Physical properties such as melting point, density, and viscosity show similar trends to boiling point in a homologous series.

The general formula of halogenoalkanes is C_nH_2n+1X.

True.

Aldehydes and ketones have the same general formula of C_nH_2nO.

False.

The general formula of an alkyne is C_nH_2n-2.

Two homologous series, with general formula, that contain nitrogen include:

• Amines - C_nH_2n+1NH₂

• Amides - C_nH_2n+1NO

The homologous series of esters has the general formula C_nH_2nO₂.

The following compound belongs to the homologous series of ethers.

Homologous series that contain a carbonyl, C=O, bond include:

• Aldehydes

• Ketones

• Carboxylic acids

• Amides

• Esters

The prefix tells you the number of carbon atoms in the longest continuous chain in the hydrocarbon.

There are three carbon atoms in the carbon chain if the prefix is prop-.

The suffix tells you what functional group is on the compound.

The name of CH₃CH₂CH₂CH₂OH is butan-1-ol.

The name of CH₃CH₂CH₂CH₂CH₃ is pentane.

The name of CH₃CH₂COOH is propanoic acid.

The name of CH₃(CH₂)₃HC=CH₂ is hex-1-ene.

False.

The name of CH₃COOCH₂CH₃ is ethyl ethanoate.

The two carbon atoms highlighted (in bold) come from the carboxylic acid used to form the ester.

False.

Numbering in organic compound names sometimes starts from the right to keep the numbers as low as possible.

Certain functional groups such as aldehydes, CHO, and carboxylic acids, COOH, normally have their carbon atom labelled as carbon-1.

The name of the following alcohol is butan-2-ol.

False.

The prefix "eth-" is used for compounds with two carbon atoms.

The prefix "prop-" is used for compounds with three carbon atoms.

An alkyl group is a hydrocarbon side chain, named by adding '-yl' to the normal alkane stem.

Multiple identical side chains are indicated by using prefixes di- (for two), tri- (for three), or tetra- (for four).

True.

In naming alkenes, the carbon atoms are numbered starting with the end closest to the double bond.

Halogenoalkanes are named using:

• The appropriate prefix fluoro-, chloro-, bromo- or iodo-, with a number to identify the carbon it is attached to in the chain

• The appropriate name to identify the longest carbon chain

• The suffix -ane to show that the halogenoalkane is saturated

The following organic compound is 3-hydroxypropanoic acid.

The carboxylic acid carbon is automatically carbon-1, which means the name ends in -oic acid.

The hydroxyl group is attached to carbon-3, which means the name starts with 3-hydroxy.

The chain is 3 carbons long and contains only single bonds, which means the name contains propan.

3-hydroxy + propan + oic acid = 3-hydroxypropanoic acid.

Isomers are compounds that have the same molecular formula but a different arrangement of atoms.

Structural isomers are compounds that have:

• The same molecular formulae

• But different structural formulae.

The three types of structural isomerism are:

1. Functional group isomerism

2. Positional isomerism

3. Branched chain isomerism.

Functional group isomerism is when different functional groups result in the same molecular formula.

True.

Alcohols and ethers can be functional group isomers of each other.

False.

Aldehydes and ketones are functional group isomers of each other.

Positional isomerism is where isomers have the same functional group in different positions on the carbon chain.

True.

Branched chain isomerism is when compounds have the same molecular formula, but their longest hydrocarbon chain is not the same.

A primary alcohol is an alcohol where the carbon atom attached to the -OH group is also attached to only one other carbon atom

False.

In amines, primary, secondary, and tertiary refer to the number of carbon atoms (or alkyl groups) attached to the nitrogen.

The smallest number of carbon atoms required for an alkane to exhibit branched chain isomerism is four.

Cyclic alkanes / cycloalkanes are functional group isomers of alkenes.

Hexan-2-ol, C₆H₁₄O, and ethoxypropane, C₅H₁₂O, are not functional group isomers of each other because they have different molecular formulae.

The positional isomer of propan-2-ol is propan-1-ol:

But-1-ene is a functional group isomer of cyclobutane and a position isomer of but-2-ene.

The branched isomer of butane is methylpropane:

The position isomer of 2-chloromethylpropane is a primary halogenoalkane because the halogen is bonded to a carbon atom that is attached to only one other carbon atom.

Stereoisomers are isomers with the same order of atoms but different spatial arrangements.

True.

Conformational isomers occur due to free rotation about a single σ-bond.

The two types of conformers in ethane are staggered and eclipsed.

Cis isomers are isomers with two functional groups on the same side of the double bond or carbon ring.

Trans isomers are isomers with two functional groups on opposite sides of the double bond or carbon ring.

True.

Cis-trans isomerism can occur in cyclic structures.

Configurational isomers are isomers with the same molecular formula and order of atoms but different shapes, which cannot be interconverted without breaking bonds.

The cis-trans naming system fails when there are more than two different atoms or groups of atoms on either side of the C=C bond.

False.

There is a difference of 60^o between staggered and eclipsed conformational isomers.

In cyclohexane, the boat conformational isomer is the least stable, as there are four eclipsed bonds causing strain on the overall structure.

The following molecule of 2,3-dichlorobut-2-ene is a trans isomer, because the chlorine atoms and methyl groups are on opposite sides of the carbon-cabron double bond, C=C.

2-bromo-1-chlorobut-1-ene cannot be named using the cis-trans naming sytem because there are three different atoms / groups of atoms.

1,1-dichlorobut-1-ene cannot be named using the cis-trans naming sytem because the chlorine atoms are bonded to the same carbon atom.

False.

Cyclic trans isomers have one functional group above the ring and one functional group below the ring.

Cyclic cis isomers have both functional groups above the ring or both functional groups below the ring.

Enantiomers are optical isomers that are non-superimposable mirror images of each other.

True.

Enantiomers have identical physical properties except for their interaction with plane-polarized light.

A racemic mixture is a mixture containing equal amounts of each enantiomer.

Optically active refers to compounds that can rotate plane polarized light.

Diastereomers are compounds that contain more than one chiral centre and are not mirror images of each other.

Racemic mixtures are optically inactive because the enantiomers cancel out each other's effect on plane polarized light.

An enantiopure compound contains only one enantiomer.

An asymmetric carbon is a carbon atom with no plane of symmetry due to having four different atoms or groups of atoms bonded to it.

The shape of a chiral carbon with four different groups attached is tetrahedral with bond angles of 109.5°.

Two reasons why many pharmaceutical drugs are sold as racemic mixtures are that separation of the enantiomers is:

• Expensive

• Time-consuming

False.

The correct 3D representation for one enantiomer of 1-chloroethan-1-ol has 2 normal bonds, 1 wedge bond and 1 dash bond:

The 3D representation for the second enantiomer of 1-chloroethan-1-ol is:

A chiral carbon is a carbon atom bonded to four different atoms or groups of atoms.

Mass spectrometry provides information on relative atomic mass, isotopes, relative molecular mass, fragments in organic compounds, and structure of organic compounds.

A molecular ion is the ion formed when a molecule loses an electron in a mass spectrometer.

The molecular ion peak represents the molecular mass of the compound being analyzed.

True.

The [M+1] peak is due to the natural abundance of the carbon-13 isotope.

Fragmentation in mass spectrometry is the process of breaking molecules into smaller ions during analysis.

The m/z value is the mass-to-charge ratio of an ion in mass spectrometry.

The peak at m/z = 18 in alcohol mass spectra indicates the loss of a water molecule.

True.

Simple alkanes are fragmented in mass spectroscopy by breaking C-C bonds.

A peak at m/z = 31 typically represents the CH₂OH⁺ fragment in alcohol mass spectra.

False.

The most abundant peak is normally one of the molecular fragments.

Fragmentation analysis in mass spectrometry helps to determine the structure of unknown compounds by identifying characteristic fragments and molecular losses.

The common fragment with an m/z value = 29 is C₂H₅⁺.

The m/z value of the C₃H₇⁺ ion is 43.

The m/z value for the [M+1] peak of propanol is 61.

Propanol has an M_r of 60, and the presence of one carbon-13 atom in the molecule increases the M_r to 61.

Possible symbol equation to show the formation of the molecular ion of propanol are:

C₃H₈O → C₃H₈O⁺ + e^-

C₃H₇OH → C₃H₇OH⁺ + e^-

Infrared spectroscopy provides information on types of covalent bonds and functional groups present in a compound.

Infrared spectroscopy is a technique used to identify compounds based on changes in the vibrations of atoms when they absorb infrared radiation of certain frequencies.

False.

Symmetrical molecules like O₂ or H₂ are IR inactive.

The fingerprint region is the area below about 1500 cm⁻¹ in an IR spectrum, which is unique to every molecule.

Resonance in infrared spectroscopy occurs when the frequency of infrared radiation matches the natural vibration frequency of a bond, causing increased amplitude of vibration.

The purpose of the fingerprint region in IR spectroscopy is to provide a unique pattern for identifying specific compounds.

A functional group in IR spectroscopy is a specific arrangement of atoms within a molecule that gives the molecule characteristic chemical properties and infrared absorption patterns.

The bond responsible for the highlighted peak is a C-O bond, with a range of 1040 - 1300 cm^-1.

The hydroxyl O-H bond is reponsible for the peak at A.

Hydroxyl O-H bonds have a characteristic scoop shape, while amine N-H bonds have a spike shape.

Alkane C-H bonds are reponsible for the peak at B.

Hydroxy C-O bonds are reponsible for the peak at C.

Carbonyl C=O bonds are reponsible for the highlighted peak.

Nuclear magnetic resonance spectroscopy is a technique used for analysing organic compounds by measuring the magnetic field strength of protons in different molecular environments.

Tetramethylsilane, TMS, is used as a reference compound in NMR spectroscopy giving a single sharp peak at a chemical shift of zero.

Chemical shift is the difference in resonance frequency between a proton in a molecule and the reference compound (TMS), measured in parts per million.

True.

The area under each peak in an NMR spectrum is proportional to the number of protons in a particular environment.

A low resolution ¹H NMR spectrum shows the intensity of each peak against their chemical shift, with each peak representing protons in the same chemical environment.

Chemically equivalent protons are protons in the same chemical environment within a molecule, which produce the same signal in an NMR spectrum.

The integration trace in an NMR spectrum shows the relative abundance of different proton environments.

False.

Only atoms with odd mass numbers show signals on NMR spectra.

Molecular environment in NMR spectroscopy refers to the specific arrangement of atoms surrounding a proton, which affects its resonance frequency and chemical shift.

The structure of tetramethylsilane is:

False.

The protons in an aldehyde and a carboxylic acid can both give peaks between 9.3 and 10.5 ppm but protons in a carboxylic acid extend beyond this range, going from 9.0- 13.0 ppm.

Three different chemical environments are present in propan-2-ol, as shown:

The expected chemical shift in the ¹H NMR spectrum for the proton highlighted of propan-2-ol is 0.5 - 6.0 ppm.

There will be three peaks seen in the ¹H NMR spectrum of cis-1-chloroprop-1-ene due to the chemical environments shown:

There are three unique hydrogen environments in the ¹H NMR spectrum.

True.

The whole number ratio of hydrogen environments is 1:3:9.

True.

The peak at around 0.9 ppm is due to a methyl group.

Peak splitting in high resolution NMR is caused by the interaction of protons with weak magnetic fields produced by neighboring protons.

Multiplicity in NMR spectroscopy is the splitting pattern of signals into sub-peaks (e.g., doublets, triplets, quartets) due to neighboring protons.

The n+1 rule in NMR peak splitting states that a signal will split into n+1 peaks, where n is the number of equivalent neighboring protons.

True.

A quartet splitting pattern indicates three neighbouring protons.

A singlet in NMR spectroscopy is an unsplit peak indicating that the proton has no neighboring protons.

A proton next to a -CH2- group would be expected to show a triplet splitting pattern.

True.

The intensity ratio of a triplet splitting pattern is 1:2:1.

The chemical shift value in an NMR spectrum indicates the general environment of the protons, helping to identify the types of functional groups present.

Shielding in NMR spectroscopy is the reduction of the effective magnetic field experienced by a nucleus due to surrounding electrons, resulting in a lower chemical shift.

True.

The shape of a quartet splitting pattern is:

Three pieces of information that are given by a ¹H NMR spectrum include:

• The number of different proton environments, from the number of signals

• The general environment of the protons, from the chemical shift values

• The relative number of protons in an environment, from the peak area

• The number of adjacent protons, from the multipicity / splitting patterns

The shape of a doublet splitting pattern is: