IUPAC Name and Structure of Straight-Chain Haloalkanes (alkyl halides) Chemistry Tutorial

Key Concepts

• Compounds containing carbon (C), hydrogen (H) and one or more halogen atoms are known as haloalkanes (or as alkyl halides⁽¹⁾).
• The term "halogen" refers to an element that belongs to the halogen group, or Group 17, of elements in the Periodic Table.

  That is, the elements fluorine (F), chlorine (Cl), bromine (Br) and iodine (I) ⁽²⁾

• In a haloalkane molecule each carbon atom atom forms a single covalent bond between itself and another carbon atom to form the parent alkane molecule.
• 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).

  halo	alkane
  prefix	stem name

• The stem (parent alkane) is determined by the number of carbon atoms making up the longest carbon chain (which includes the halogen atoms that have substituted for hydrogen atoms).

  Number of Carbon atoms in the chain	1	2	3	4	5		7	8	9	10
  stem (parent alkane)	methane	ethane	propane	butane	pentane	hexane	heptane	octane	nonane	decane

• The prefix is determined by the number and type of halogen atoms that occur along the parent alkane chain (the longest carbon chain) and is made up of three parts; an infix, a multiplier, and the modified name of the halogen element(s):

  prefix
  infix-	multiplier	modified halogen name

  The infix is a number (or numbers) that tell us the location of each halogen atom along the carbon chain.

  If more than one atom of the same halogen element is present in the molecule:

  (i) Each number in the infix is separated from other numbers in the infix by a comma (,)
  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.

  (ii) A multiplier precedes the name of the halogen atom:

  <

  Number of identical halogen atoms	2	3	4	5	6	7	8
  multiplier prefix	di	tri	tetra	penta	hexa	hepta	octa

  If only one atom of the halogen element is present in the molecule no multiplier is used.

  A hyphen (-) separates the infix from the multiplier (or separates the infix from the name of the halogen atom if only one atom of the halogen is present).

  The modified name of the halogen used in the prefix is constructed by dropping the "ine" ending of the halogen's name and adding "o":

  Symbol of Element	Name of Element	remove "ine"	add "o"
  F	fluorine	fluor	fluoro
  Cl	chlorine	chlor	chloro
  Br	bromine	brom	bromo
  I	iodine	iod	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

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Structure and Bonding in Haloalkanes (alkyl halides)

• Carbon belongs to group 14 of the periodic table.

  Each carbon atom in the haloalkane (alkyl halide) molecule has 4 valence electrons.

  	.
  .	C	.
  	.

• Each hydrogen atom in the haloalkane (alkyl halide) molecule has 1 valence electron.

  .

  H

• Halogen atoms are found in Group 17 of the periodic table.

  Each halogen atom (X) in the haloalkane (alkyl halide) molecule has 7 valence electrons.

  	..
  .	X	:
  	..

  Where X is the symbol of a halogen atom, that is, F, Cl, Br or I

  Note that a halogen atom can complete its octet of valence electrons by sharing its unpaired electron with another atom such as carbon.

• Each carbon atom in the parent alkane molecule makes 4 covalent bonds by sharing a valence electron with another atom to make an octet of electrons (4 electron pairs).

  Lewis Structure (electron dot diagram)		Valence Structure
  .   .   . . C . .   .   .		|   - C -   |

• Each carbon atom can covalently bond to other carbon atoms, hydrogen atoms, or halogen atoms:

  	C-C		C-H		C-X
  Lewis Structure	. . C . .. . C . .		. . C . .. H		. . C . .. .. X .. :
  Valence Structure	. . C . - . C . .		. . C . - H		. . C . - .. X .. :

• In the straight-chain parent alkane molecule of a haloalkane (alkyl halide) there are only single covalent bonds made up of one pair of electrons joining one carbon atom to another carbon atom.

  Lewis Structure (electron dot diagram)		Valence Structure
  .   .   .   . C .. C .. C .   .   .   .		.   .   .   . C - C - C .   .   .   .

• In order to complete the octet of electrons around each carbon atom, any unpaired electron will pair up with the valence electron from an atom of hydrogen to form the parent alkane molecule.

  Lewis Structure (electron dot diagram)		Valence Structure
  H   H   H         . .   . .   . .     H .. C .. C .. C .. H     . .   . .   . .         H   H   H		H   H   H         |   |   |     H - C - C - C - H     |   |   |         H   H   H

• In the haloalkane (alkyl halide) molecule, any or all of the hydrogen atoms (H) in the parent alkane molecule can be substituted for a halogen atom (X):

  Some possible haloalkane (alkyl halide) molecules can then be represented as shown below:

  Lewis Structure (electron dot diagram)		Valence Structure
  H   H   H           . .   . .   . .   .. H .. C .. C .. C .. X:     . .   . .   . .   ..     H   H   H		H   H   H           |   |   |   .. H - C - C - C - X:     |   |   |   ..     H   H   H
  H   .. :X:     H           . .   . .   . .     H .. C .. C .. C .. H     . .   . .   . .         H   H   H		H   .. :X:     H           |   |   |     H - C - C - C - H     |   |   |    '     H   H   H
  H   .. :X:     H           . .   . .   . .   .. H .. C .. C .. C .. X:     . .   . .   . .   ..     H   H   H		H   .. :X:     H           |   |   |   .. H - C - C - C - :X:     |   |   |   ..     H   H   H

Steps for IUPAC Naming of Straight-Chain Haloalkanes (alkyl halides)

The systematic IUPAC name for a straight-chain haloalkane is made up of a prefix and a stem.

The stem is determined by the number of carbon atoms making up the longest carbon chain (which includes the halogen atoms that have substituted for hydrogen atoms).

The prefix is determined by the number and type of halogen atoms that occur along the parent alkane chain (the longest carbon chain).

Step 1: Identify and name the longest carbon chain containing the halogen atoms.

Name the carbon chain as you would for an alkane molecule:

Step 2: Identify and name each halogen atom present in the molecule:

Step 3: If more than one type of halogen atom is present, list the halo prefixes in ascending alphabetical order from left to right:

Step 4: If more than one atom of the same halogen element is present, modify the halo prefix using the appropriate multiplier prefix:

Step 5: Add the multiplier prefix to the name of the halogen atom as written in the order given in Step 3 above.

If only one atom of a particular halogen atom is present, no multiplier is included for this atom.

DO NOT change the order!

Step 6: Number the carbon atoms in the parent alkane chain so that the halogen atoms are attached to the carbon atoms with the lowest set of numbers.

The lowest set of numbers is that which, when compared term by term in the order given above, has the lowest term at the first point of difference.

Example: 1-bromo-2-chloroethane NOT 2-bromo-1-chloroethane

Step 7: Use the number of the carbon atom to which each halogen is attached as an infix for that modified prefix.

Note: The modified prefix representing each halogen atom must be preceded by a number.

If the modified prefix does not include a multiplier (that is only one atom of this halogen element is present), one number will precede the prefix.
If the modified prefix includes a multipler prefix, then the number of numbers is the same as indicated by the multiplier prefix
di means there must be two numbers preceding the prefix, tri means there must be three numbers preceding the prefix, etc

Note, numbers for each halogen atom are written in ascending order.

Numbers making each infix are separated from each other by a comma (,)
Numbers making up each infix are separated from words (or word fragments) by hyphens (-)

Step 8: Assemble the final name.

Write the out the string of infix-multiplierhalo prefixes in alphabetical order with a hyphen (-) between word fragments and numbers:

infix-multiplierbromo-infix-multiplierchloro-infix-multiplierfluoro-infix-multiplieriodo

Write the name of the parent alkane (determined in Step 1 above) directly after the last halogen element's prefix.

DO NOT leave a space between the name of the halogen prefix and the alkane's name.

infix-multiplierbromo-infix-multiplierchloro-infix-multiplierfluoro-infix-multiplieriodoalkane

Worked Example: IUPAC Naming of Haloalkane with a Single Substitution

Name the haloalkane molecule shown below using systematic IUPAC nomenclature rules:

Step 1: Identify and name the longest carbon chain containing the halogen atoms.

Longest carbon chain has 3 carbon atoms.

propane is the name of the alkane with 3 carbon atoms.

Stem = propane

Step 2: Identify and name each halogen atom present in the molecule:

Cl is the symbol for the halogen element chlorine.

prefix is chloro

Step 3: If more than one type of halogen atom is present, list the halo prefixes in ascending alphabetical order from left to right:

Only one type of halogen atom is present, that is, just chlorine.

prefix is still chloro

Step 4: If more than one atom of the same halogen element is present, modify the halo prefix using the appropriate multiplier prefix:

Only one chlorine atom is present.

prefix is still chloro

Step 5: Add the multiplier prefix to the name of the halogen atom as written in the order given in Step 3 above.

No multiplier prefix is required because only one atom of chlorine is present.

prefix is still chloro

Step 6: Number the carbon atoms in the parent alkane chain so that the halogen atoms are attached to the carbon atoms with the lowest set of numbers

Numbering from right to left results in the chlorine atom being attached carbon 1 rather than carbon 3 (as when the chain is numbered from left to right).

The preferred numbering is therefore from right to left because it results in the lowest number for the infix.

Step 7: Use the number of the carbon atom to which each halogen is attached as an infix for that modified prefix.

chlorine atom attached to carbon 1 :

infix-prefix is 1-chloro

Step 8: Assemble the final name: add the prefix to the name of the parent alkane

1-chloropropane

Worked Example: IUPAC Naming of Haloalkane with Multiple Substitutions of the Same Halogen

Name the haloalkane molecule shown below using systematic IUPAC nomenclature rules:

Step 1: Identify and name the longest carbon chain containing the halogen atoms.

Longest carbon chain has 3 carbon atoms.

propane is the name of the alkane with 3 carbon atoms.

Stem = propane

Step 2: Identify and name each halogen atom present in the molecule:

Br is the symbol for the halogen element bromine.

prefix is bromo

Step 3: If more than one type of halogen atom is present, list the halo prefixes in ascending alphabetical order from left to right:

Only one type of halogen atom is present, that is, just bromine.

prefix is still bromo

Step 4: If more than one atom of the same halogen element is present, modify the halo prefix using the appropriate multiplier prefix:

Three bromine atoms are present.

multiplier prefix is tri

Step 5: Add the multiplier prefix to the name of the halogen atom as written in the order given in Step 3 above.

multiplier prefix is tri

modified bromo prefix is now tribromo

Step 6: Number the carbon atoms in the parent alkane chain so that the halogen atoms are attached to the carbon atoms with the lowest set of numbers

The preferred numbering is from right to left because it results in the lowest set of numbers for the infix (1,2,2 instead of 2,2,3).

Step 7: Use the number of the carbon atom to which each halogen is attached as an infix for that modified prefix.

bromine atoms attached to carbons 1,2,2

infix-prefix is 1,2,2-tribromo

Step 8: Assemble the final name: add the prefix to the name of the parent alkane

1,2,2-tribromopropane

Worked Example: IUPAC Name of Haloalkane With Substitution by More Than One Type of Halogen Atom

Name the haloalkane molecule shown below using systematic IUPAC nomenclature:

Step 1: Identify and name the longest carbon chain containing the halogen atoms.

Longest carbon chain has 3 carbon atoms.

propane is the name of the alkane with 3 carbon atoms.

Stem = propane

Step 2: Identify and name each halogen atom present in the molecule:

Cl is the symbol for chlorine, modified name to be used in the prefix is chloro

Br is the symbol for bromine, modified name to be used in the prefix is bromo

Step 3: If more than one type of halogen atom is present, list the halo prefixes in ascending alphabetical order from left to right:

bromo     chloro

("b" from bromo comes before "c" from chloro in the alphabet)

Step 4: If more than one atom of the same halogen element is present, modify the halo prefix using the appropriate multiplier prefix:

two bromine atoms, multiplier to use is di

one chlorine atom, no multiplier is used

Step 5: Add the multiplier prefix to the name of the halogen atom as written in the order given in Step 3 above.

dibromo     chloro

Step 6: Number the carbon atoms in the parent alkane chain so that the halogen atoms are attached to the carbon atoms with the lowest set of numbers

The preferred numbering is from right to left because it results in the lowest set of numbers for the infixes.

That is infex 1,2 for bromine atoms and 2 for chlorine atom (rather than 2,3 for bromine and 2 for chlorine)

Step 7: Use the number of the carbon atom to which each halogen is attached as an infix for that modified prefix.

Remember, numbers are separated from numbers by commas, numbers are separated from letters by hyphens, and, there are no spaces!

1,2-dibromo-2-chloro

Step 8: Assemble the final name: add the prefix to the name of the parent alkane

Remember there are no spaces in the final name!

1,2-dibromo-2-chloropropane

Steps for Drawing the Structure⁽⁴⁾ of Straight Chain Haloalkanes

Step 1: Break the name of the haloalkane up into two parts: prefix and stem (the name of the parent alkane)

Step 2: Determine the number of carbon atoms in the parent alkane from the stem.

Step 3: Draw the parent alkane showing all carbon atoms and covalent bonds.

Remember that there are only single covalent bonds between the carbon atoms in an alkane molecule.

Do not show hydrogen nor halogen atoms.

Step 4: Break the prefix of the haloalkane's name up into "infix-multiplierhalo" segments.

Step 5: Determine the number and type of each halogen atom present using each "multiplierhalo" segment.

Step 6: Determine the location of each halogen atom using the infix for each segment.

Step 7: Number the carbon atoms in this parent alkane molecule in ascending order from left to right.

Step 8: Position each halogen atom along the chain in the location indicated by the infix for each segment.

Step 9: Complete the structure by placing a hydrogen atom (H) at the end of any vacant covalent bond.

Worked Example of Drawing the Structure of a Haloalkane (alkyl halide)

Draw the structure for 1,2-dibromo-1-chloro-1-fluoroethane

Step 1: Break the name of the haloalkane up into two parts: prefix and stem (the name of the parent alkane)

Step 2: Determine the number of carbon atoms in the parent alkane from the stem.

stem is ethane (name of the parent alkane)

eth = 2 carbon atoms

Step 3: Draw the parent alkane showing all carbon atoms and covalent bonds.

Remember that there are only single covalent bonds between the carbon atoms in an alkane molecule.

Do not show hydrogen nor halogen atoms.

Step 4: Break the prefix of the haloalkane's name up into "infix-multiplierhalo" segments.

There are three "infix-multiplierhalo" segments in the name of this molecule:

(i) 1,2-dibromo

(ii) 1-chloro

(iii) 1-fluoro

Step 5: Determine the number and type of each halogen atom present using each "multiplierhalo" segment.

(i) 1,2-dibromo = two Br atoms (di multiplier = two atoms of this halogen)

(ii) 1-chloro = one Cl atom (no multiplier means there is only one atom of this halogen)

(iii) 1-fluoro = one F atom (no multiplier means there is only one atom of this halogen)

Step 6: Determine the location of each halogen atom using the infix for each segment.

(i) 1,2-dibromo : one Br atom is located on carbon 1, one Br atom is located on carbon 2

(ii) 1-chloro : one Cl atom is located on carbon 1

(iii) 1-fluoro : one F atom is located on carbon 1

Step 7: Number the carbon atoms in this parent alkane molecule in ascending order from left to right.

Step 8: Position each halogen atom along the chain in the location indicated by the infix for each segment.

Step 9: Complete the structure by placing a hydrogen atom (H) at the end of any vacant covalent bond.

Summay Table 1: IUPAC Name and Structure of Some Single Substitution Haloalkanes

Summay Table 2: IUPAC Name and Structure of Some dihaloalkanes (same halogen type)

Summay Table 3: IUPAC Name and Structure of Some dihaloalkanes (different halogen type)