M7 OC1 Naming

IQ1. How do we systematically name organic chemical compounds?

1.1 The nomenclature of organic chemicals

1.2 Structural isomers

Wonder why we need a separate naming system for carbon compounds? This is chlorophyll

• chemical formula: C55H72MgN4O5
• chemical name: methyl (3R,21S,22S)-16-ethenyl-11-ethyl-12,17,21,26-tetramethyl-4-oxo-22-[3-oxo-3-[(E,7R,11R)-3,7,11,15-tetramethylhexadec-2-enoxy]propyl]-23,25-diaza-7,24-diazanidahexacyclo[18.2.1.15,8.110,13.115,18.02,6]hexacosa-1,5,8(26),9,11,13(25),14,16,18,20(23)-decaene-3-carboxylate :

1. How do we systematically name organic chemical compounds?

7.1 Nomenclature

7.1a The nomenclature of organic chemicals

7.1b Structural isomers

Wait a minute, before we learn to name organic compounds, we need a summary of the different ways to write and draw formulas for the compounds:

The molecular formula of a compound gives the exact number of each different type of atom (i.e. type of element) present in one molecule of the compound. This is useful because it allows you to work out the molecular weight of the compound, but doesn’t give you any information about the bonds in the molecule, and might not even tell you about which functional groups are present (functional groups are the parts of the organic molecule that dictate its particular reactivity with other chemicals.)

The empirical formula is the simplest ratio of the elements present in a molecule. They are of some use for organic compounds – they can sometimes help us work out the molecular formula if we don’t know it. (They are much more frequently used for ionic compounds, such as table salt, sodium chloride (NaCl). Ionic compounds have giant lattice structures – a large number of oppositely charged ions electrostatically attracted to each other. It wouldn’t be practical to try and write down the exact number of each type of atom present in a crystal of salt, because the number would be huge – so we just use the simple empirical formula instead.)

The condensed formula is often used in text. Each carbon in the molecule is written out in turn, with the atoms attached to it written directly after. Brackets are used to indicate branching in the molecule, or multiple identical groups. This is more often seen for organic acids when writing acid-base chemical equations since it highlights the acid functional group.

The displayed formula represents the molecule by showing all of the atoms, and all of the bonds between those atoms. Bonds are represented by lines, with the number of lines representing the strength of the bond. Single bonds and double bonds (2 lines) are relatively common, but triple bonds (3 lines) are also possible in some molecules. These are obviously useful, in that they show the molecule in as much detail as possible, but they also take up a lot of space, and can be time-consuming to draw. The structural formula attempts to tackle this by omitting some bonds, and grouping some atoms together, but still isn’t the quickest way to represent an organic molecule.

The skeletal formula is the simplest way of representing organic molecules, and so is commonly seen in both textbooks and research publications. It represents the main carbon chain as a zig-zag line, where the end of lines and the vertices (points) represent carbon atoms. All hydrogens are omitted, unless they are part of a functional group (eg -OH, COOH), when they are always shown; atoms other than carbon or hydrogen are also always shown.

The general formula doesn’t apply to just one compound. It applies to families of compounds; it gives a way to predict the molecular formula of a compound based on the number of carbons it contains. For an alkane the general formula is C_nH_2n+2. This means that if you know the number of carbons, you just need to multiply that number by two, then add two, to find the number of hydrogens. Every simple organic molecule has a general formula that can be used to work out the molecular formula of particular members of that family of compounds.

We have heard unofficially that NESA is now going with the IUPAC (International Union of Pure and Applied Chemists) change to nomenclature (naming). The new system (2017) was not previously incorporated into RACI (Royal Australian Chemical Institute) naming, but now is. The link below gives naming. There is still confusion over what is expected among Chem teachers, but we will sort it out soon. In the mean time, we will stick with simple and move to more complex if it is needed.

View Videos:

• OC#1a Naming alkanes https://www.youtube.com/watch?v=RithnyHEFtQ [8.56]

Branched-chain Alkanes

Not all alkanes have the carbon atoms in one single chain. Some have carbon atoms that branch off. (These are called chain isomers, covered in 1.2.0 They are named by

1. finding the longest chain that doesn't include the atoms in the branches,
2. naming the branches (number of carbon atoms) with an -yl ending,
3. numbering the places they come off the chain, eg 3-methylhexane is shown below.

More information on naming branched alkanes is given in the box following the diagram below.

View Videos:

• OC#1b Naming alkenes https://www.youtube.com/watch?v=MXdEJDa-JIg [5.18]

ALKENES

Alkenes are hydrocarbons, molecules made up of only carbon and hydrogen atoms, in which there is a double bond between two carbon atoms -C=C-

The general molecular formula for a straight-chain alkene is C_nH_2n, where n = number of carbon atoms in the carbon chain.

The systematic IUPAC name of a straight-chain alk-n-ene is made up of three parts⁽³⁾:

• (i) A prefix which tells us how many carbon atoms are in the chain (alk).
• (ii) An infix number which is a number that tells us the location of the double bond (-n-)
• (iii) The suffix ene telling us that a double bond is present within the chain.

Naming Straight-Chain Alkenes:

• Identify the number of carbons in the carbon chain .
• Determine the prefix for the name of the alkene based on that number.
• Number each carbon atom along the carbon chain so that the first of the double bonded carbon atoms has the lowest possible number.
• Determine the infix number for the name of the alkene based on the location of the double bond (use the lowest number out of the two carbon atoms joined by the double bond).
• Note that the infix will not be required for ethene or propene.
• Determine the suffix: end in "ene".
• Write the name for the alkene in the form of prefix-number-suffix

View Videos:

• OC#1b Naming alkyenes https://www.youtube.com/watch?v=MXdEJDa-JIg&t=1s [5.19]

ALKYNES

Alkynes are hydrocarbons, molecules made up of only carbon and hydrogen atoms, in which there is a triple bond between two carbon atoms

The general molecular formula for a straight-chain alkyne is C_nH_2n-2, where n = number of carbon atoms in the carbon chain.

The systematic IUPAC name of a straight-chain alk-n-yne is made up of three parts⁽³⁾:

• (i) A prefix which tells us how many carbon atoms are in the chain (alk).
• (ii) An infix number which is a number that tells us the location of the triple bond (-n-)
• (iii) The suffix yne telling us that a triple bond is present within the chain.

Naming Straight-Chain Alkynes:

• Identify the number of carbons in the carbon chain .
• Determine the prefix for the name of the alkyne based on that number.
• Number each carbon atom along the carbon chain so that the first of the triple bonded carbon atoms has the lowest possible number.
• Determine the infix number for the name of the alkyne based on the location of the triple bond (use the lowest number out of the two carbon atoms joined by the triple bond).
• Note that the number will not be required for ethyne or propyne.
• Determine the suffix: end in "yne".
• Write the name for the alkyne in the form of prefix-number-suffix

View Videos:

• OC#1c Naming alkynes https://www.youtube.com/watch?v=AWxD20v0eCU&t=34s [3.47]

ALCOHOLS (ALKANOLS)

Alkanols

• are organic molecules containing only carbon (C), hydrogen (H) and oxygen (O) atoms.
• are hydroxy compounds, they contain an -OH [hydroxy (or hydroxyl)] functional group.
• A straight-chain alkanol consists of 1 or more carbon atoms joined to each other in a chain by single covalent bonds, with an -OH functional group attached to one of the carbon atoms in the chain.

The general molecular formula for a straight-chain alkanol is C_nH_2n+2O where n = number of carbon atoms in the carbon chain.

The systematic IUPAC name of an alkan-n-ol is made up of three parts:

• (i) a prefix or stem (the name of the parent hydrocarbon (the alkane chain) without the "e" ending, alkan)
• (ii) an infix (a number which tells us the location of the OH functional group, -n-), [only necessary for propanol or longer chains]
• (iii) a suffix (last part of the name, ol). The suffix when naming a straight-chain alkanol is always "ol"

The prefix or stem is dependent on the number of carbon atoms in the longest chain of carbon atoms (the parent hydrocarbon, or parent alkane) containing the -OH group.

Example: propan-1-ol and propan-2-ol

Note the examples below: These two drawings are for the same molecule, just turned around. There can only be one name, so the one with the lower number is correct (not just preferred!!!).

View videos:

• OC#2 Naming alcohols https://www.youtube.com/watch?v=Gfv-hD1nYLA [11.34 mins]

ALDEHYDES (ALKANALS)

Alkanals are organic molecules containing only carbon (C), hydrogen (H) and oxygen (O) atoms. They belong to the group of organic compounds known as aldehydes. The general molecular formula for a straight-chain alkanal is C_nH_2nO, where n = number of carbon atoms in the carbon chain.

• Aldehydes consist of a chain of 1 or more carbon atoms joined to each other by single covalent bonds, with a C=O (carbonyl) functional group attached to the terminal (end) carbon atom in the chain of carbon atoms.
• The systematic IUPAC name of an alkanal is made up of two parts:

(i) a prefix or stem

(ii) a suffix (last part of the name, al)

• The prefix or stem is dependent on the number of carbon atoms in the longest chain of carbon atoms (the parent hydrocarbon, or parent alkane).

KETONES (ALKANONES)

Alkanones are organic molecules containing only carbon (C), hydrogen (H) and oxygen (O) atoms.

Alkanones belong to the group of organic compounds known as ketones. The general molecular formula for a straight-chain alkanone is C_nH_2nO, where n = number of carbon atoms in the carbon chain.

Ketones contain a C=O, carbonyl, functional group. Ketones consist of a chain of 3 or more carbon atoms joined to each other by single covalent bonds, with a =O attached to a non-terminal carbon atom in the chain of carbon atoms.

The systematic IUPAC name⁽²⁾ of an alkan-n-one is made up of three parts:

• (i) a prefix or stem dependent on the number of carbon atoms in the longest chain of carbon atoms (the parent hydrocarbon, or parent alkane
• (ii) an infix number (location of C=O along the chain)
• (iii) a suffix one (which sounds like "own" not like "won")

Note that it is not possible to construct an alkanone with only 1 or 2 carbon atoms in the chain, because, in both these cases, the carbonyl functional group would occur on a terminal (end) carbon atom so the molecules would be alkanals (aldehydes) NOT alkanones (ketones). Propanone is therefore the first possible member of the alkanone homologous series.

View videos:

• OC#3 Naming adehydes and ketones https://www.youtube.com/watch?v=kDPYPG5h0uM&list=PLeFSFSJ9WqSDRKZVcK33Gtz60RsJ5_t7Q&index=6 [9.10 mins]

CARBOXYLIC ACIDS (Alkanoic Acids)

Alkanoic acids are organic molecules containing only carbon (C), hydrogen (H) and oxygen (O) atoms. Alkanoic acids belong to the group of organic compounds known as carboxylic acids.

All alkanoic acids contain the carboxyl (COOH) functional group. The general molecular formula for a straight-chain alkanoic acid is C_nH_2nO_2, where n = number of carbon atoms in the carbon chain.

A straight-chain alkanoic acid consists of a chain of 1 or more carbon atoms joined to each other by single covalent bonds, with an OH and a =O functional group attached to a terminal (end) carbon atom in the chain.

Numbering of the carbon chain begins with the carbon atom of the carboxyl functional group. The systematic IUPAC name of an alkanoic acid is made up of two parts:

• (i) a prefix or stem (the name of the parent hydrocarbon (the alkane chain without the "e" ending, alkan)
• (ii) a suffix (last part of the name, oic acid)

View videos:

• OC#4 Naming carboxylic acids https://www.youtube.com/watch?v=vdBspcssTGg&list=PLeFSFSJ9WqSDRKZVcK33Gtz60RsJ5_t7Q&index=7 [6.09 mins]

AMINES

Amines are organic molecules containing only carbon (C), hydrogen (H) and nitrogen (N) atoms. Amines are derivatives of ammonia, NH₃, in which carbon chains replace hydrogen atoms.

Primary alkanamines occur when only one of the hydrogen atoms in ammonia has been replaced by a carbon chain. They contain the NH₂ (amine, amino) functional group R-NH₂

A primary alkanamine consists of a chain of 1 or more carbon atoms joined to each other by single covalent bonds, with an NH₂ functional group attached to one of the carbon atoms in the chain.

The systematic IUPAC name⁽²⁾ of an alkan-n-amine is made up of three parts:

• (i) a prefix or stem (the name of the parent hydrocarbon (the alkane chain) without the "e" ending, alkan), dependent on the number of carbon atoms in the longest chain of carbon atoms (the parent hydrocarbon, or parent alkane
• (ii) an infix number (which tells us the location of the NH₂ functional group, -n-)
• (iii) a suffix (last part of the name, amine)

AMIDES (ALKANAMIDES)

Amides are organic molecules containing only carbon (C), hydrogen (H) and nitrogen (N) atoms. Amides are named as derivatives of the corresponding carboxylic acid.

In primary alkanamides, an NH₂ group replaces the OH group in the alkanoic acid. Primary alkanamides contain the C(O)-NH₂ (amide) functional group. A primary alkanamide consists of a chain of 1 or more carbon atoms joined to each other by single covalent bonds, with the amide, C(O)-NH₂, functional group attached to the first carbon atom in the chain.

The systematic IUPAC name of a primary amide is made up of two parts:

• (i) a prefix or stem (the name of the parent alkanoic acid without the "oic acid" ending, alkan)
• (ii) a suffix (last part of the name, amide)

View videos:

• OC#5 Naming amines and amides https://www.youtube.com/watch?v=_1J4sukzA7g&list=PLeFSFSJ9WqSDRKZVcK33Gtz60RsJ5_t7Q&index=8 [9.57 mins]

Haloalkanes (alkyl halides)

Compounds containing carbon (C), hydrogen (H) and one or more halogen atoms are known as haloalkanes (or as alkyl halides). The term "halogen" refers to an element that belongs to the halogen group, Group 17, of elements in the Periodic Table; fluorine (F), chlorine (Cl), bromine (Br) and iodine (I)

In a haloalkane molecule some, or all, of the hydrogen atoms in the parent alkane molecule are replaced with halogen atoms.

The preferred systematic IUPAC name⁽³⁾ for a straight-chain haloalkane is made up of a prefix and a stem (name of the parent hydrocarbon). The prefix is determined by the number and type of halogen atoms that occur along the parent alkane chain (the longest carbon chain).

Example: 1,1-dibromo-2-chloro-2-fluoro-4-iodooctane

The prefix (in bold above) is made up of three parts:

• infix number (or numbers) that tell us the location of each halogen atom along the carbon chain, with each number separated from other numbers by a comma, and the numbers separated from the multiplier by a hyphen (-)
  • the lowest set of numbers is used, that is, the set of numbers which, when compared term by term as written with other sets, has the lowest term at the first point of difference (explained below)
• multiplier (if more than one atom of the same halogen element is present in the molecule) precedes the name of the identical halogen atoms: two=di, three=tri, four=tetra, five=penta, etc,
• modified name of the halogen - constructed by dropping the "ine" ending of the halogen's name and adding "o":
  • F fluorine fluoro
  • Cl chlorine chloro
  • Br bromine bromo
  • I iodine iodo
• The name of the haloalkane is then constructed by placing the prefixes in ascending alphabetical order based on the name of the halogen before the name of the parent alkane: bromo named before chloro named before fluoro named before iodo
• infix-multiplierbromo-infix-multiplierchloro-infix-multiplierfluoro-infix-multiplieriodoalkane
  • There are no spaces in the final name!
  • Numbers are separated by numbers using commas
  • Numbers are separated from words (or word fragments) using hyphens
  • There are no spaces between letters nor between words or word fragments

View videos:

• OC#6 Naming halogenated organic compounds https://www.youtube.com/watch?v=2XUc9yHkQh4&list=PLeFSFSJ9WqSDRKZVcK33Gtz60RsJ5_t7Q&index=9 [11.48 mins]

ISOMERS

(ISO=EQUAL, MER=PART)

View videos:

• OC#7 Isomerism https://www.youtube.com/watch?v=isf_-rjiGUE&list=PLeFSFSJ9WqSDRKZVcK33Gtz60RsJ5_t7Q&index=10 [17.27 mins]

View videos:

• OC#7a Chain Isomerism https://www.youtube.com/watch?v=RoyQNkQID18&list=PLeFSFSJ9WqSDRKZVcK33Gtz60RsJ5_t7Q&index=11 [3.58 mins]

View videos:

• OC#7b Position Isomerism https://www.youtube.com/watch?v=21QxikJCb5Y&list=PLeFSFSJ9WqSDRKZVcK33Gtz60RsJ5_t7Q&index=12 [4.12 mins]

View videos:

• OC#7c Functional Group Isomerism https://www.youtube.com/watch?v=8MYN6ckrAGk&list=PLeFSFSJ9WqSDRKZVcK33Gtz60RsJ5_t7Q&index=13 [5.01 mins]

Homologous series are groups of compounds which are characterised by

• a common general formula
• a common functional group
• similar structures and chemical properties
• gradations in their physical properties (as MM increases)

Alkanes

These contain only single carbon-carbon bonds (functional group) and are thus called

saturated hydrocarbons. Their general formula is: CnH2n+2, or R1(CH2)nR2 where R1 and R2 are either H or an alkyl group

The alkanes are the principle compounds in natural gas and petroleum. The C — C single bond is extremely stable and so saturated hydrocarbons are relatively inert.

One important reaction however is their combustion reactions where they are important

fuels. They all burn in sufficient air or oxygen to produce carbon dioxide and water.

Alkenes

These contain a double carbon = carbon bond (functional group) at least once in the main

carbon chain of the molecule and single carbon-carbon bonds elsewhere. Their general formula is CnH2n or R1CH = CHR2 where R1 and R2 are either H or an alkyl group

Alkynes

These contain a triple carbon ≡ carbon bond (functional group) at one end (1-alkyne) of the molecule and single carbon-carbon bonds elsewhere. Their general formula is CnH2n-2 or R1C ≡ CR2 where R1 and R2 are either H or an alkyl group

Unsaturated

Both alkenes and alkynes are called unsaturated hydrocarbons as they can react by addition reactions at the double or triple bond to combine with more atoms as single bonds are produced.

All hydrocarbon series can exist as long chains or rings. If a hydrocarbon has a number of carbons joined together to form an enclosed ring, we use the prefix ‘cyclo’ to indicate this circle or ring structure, eg cyclobutane. NB Cyclic forms will not conform to the general formula for their homologous series.