IUPAC Nomenclature Notes (Page-by-Page)

Page 1

  • Topic: How to Name Alkanes, Alkyl Halides, and Alcohols using the IUPAC System.
  • IUPAC system: one of the most commonly used nomenclature systems today.
  • Fundamental principle: Each different compound shall have a unique name.
  • Emphasis: IUPAC system provides a universal, unambiguous naming method for organic compounds.

Key terms:

  • IUPAC = International Union of Pure and Applied Chemistry.
  • Nomenclature = system for naming chemical compounds.

Significance:

  • Enables precise communication in science and commerce across languages and regions.

Page 2

  • While IUPAC names are standard, common (trivial) names are still widely used by chemists and in commerce.
  • Learning common names for frequently used chemicals can be important for practical understanding and communication.

Page 3

  • Alkanes: general formula CnH{2n+2}.
    • Example: hexane with formula C6H{14}.
  • Cycloalkanes: general formula CnH{2n}.
    • Example: cyclohexane with formula C6H{12}.
  • Distinguishing feature: Alkanes are open-chain; cycloalkanes contain rings.

Page 4

  • The common alkane name ending: -ane.
  • The names of most alkanes derive from Greek/Latin roots:
    • 1 → meth- (methyl), 2 → eth- (ethyl), 3 → prop- (propyl), 4 → but- (butyl), 5 → pent- (pentyl).
  • This page emphasizes the root system used for straight-chain alkanes.

Page 5

  • Provides a quick reference of simple alkanes and their structures in the unbranched series:
    • Methane: ext{CH}_4
    • Ethane: ext{CH}3 ext{CH}3
    • Propane: ext{CH}3 ext{CH}2 ext{CH}_3
    • Butane: ext{CH}3 ext{CH}2 ext{CH}2 ext{CH}3
    • Pentane: ext{CH}3( ext{CH}2)3 ext{CH}3
    • Hexane: ext{CH}3( ext{CH}2)4 ext{CH}3
    • Heptane: ext{CH}3( ext{CH}2)5 ext{CH}3
    • Octane: ext{CH}3( ext{CH}2)6 ext{CH}3
    • Nonane: ext{CH}3( ext{CH}2)7 ext{CH}3
    • Decane: ext{CH}3( ext{CH}2)8 ext{CH}3
  • Note: The slide also lists cycloalkanes like cyclohexane with formula C6H{12} as part of the broader alkane family.

Page 6

  • 3A. How to Name Unbranched Alkyl Groups.
  • Alkyl group defined as the removal of one hydrogen atom from an alkane.

Page 7

  • Alkyl group (continued):
    • Methane yields methyl group (Me).
    • Ethane yields ethyl group (Et).
    • Propane yields propyl group (Pr).
  • Diagrammatic note: removing a terminal hydrogen from the corresponding alkane yields the alkyl group.

Page 8

  • 3B. How to Name Branched-Chain Alkanes – Rule 1:
    • Use the longest continuous carbon chain as the parent name.
    • Example sketches show branches such as 3-methylheptane and 2-ethylhexane.

Page 9

  • Rule (Cont’d):
    • After selecting the longest chain, apply Rule 2 to designate the location of the substituent(s).
    • The rule set also emphasizes choosing the lowest possible locants for substituents.
  • Examples illustrate how numbering is chosen to minimize substituent positions.

Page 10

  • Rule 4 (in the course of rules for substituents):
    • For two or more substituents, use the lowest possible individual numbers for the parent chain.
    • Substituents should be listed in alphabetical order.
    • In alphabetizing, disregard multiplying prefixes like di-, tri-, etc.

Page 11

  • Example illustrations of naming with multiple substituents, showing how to assign numbers and order:
    • Example name like (6-Ethyl-2-methyloctane) is given.
    • The “NOT” figures indicate numbers that would be incorrect under the rules.

Page 12

  • Rule 5: When two substituents appear on the same carbon, use that number twice (e.g., 4-ethyl-4-methyloctane).

Page 13

  • Rule 6: For identical substituents, use prefixes di-, tri-, tetra-, etc. (e.g., 2,4-dimethylhexane).
  • Examples show how to place multiple identical substituents on the parent chain with correct numbering.

Page 14

  • Rule 7: When two chains have equal length, prefer the chain with more substituents as the parent.
  • Example: a tricyclic scenario showing 2,3,5-trimethyl-4-propylheptane as a preferred name over a chain with fewer substituents.

Page 15

  • Rule 8: When branching starts at equal distances from either end of the longest chain, choose the name that gives the lower number at the first point of difference.
  • Demonstrated with a comparison of two naming options.

Page 16

  • Example 1 (Find the longest chain as parent): shows a structure with several possible parent chains; choose the longest chain as the parent.

Page 17

  • Example 1 (Cont’d): two methyl substituents (dimethyl) on the chosen chain; use the lowest possible numbering for the substituents.
  • Finalization leads to a name such as dimethylheptane with the correct numbering.

Page 18

  • Example 1 (Cont’d): complete name for the given structure is (3,4-Dimethylheptane).

Page 19

  • Example 2 introduction (longer chain): appears to set up a second naming example with different substituents.

Page 20

  • Example 2 (Cont’d): process begins with determining whether a longer chain exists or if a different parent should be chosen; starting with a 6-carbon chain in the first impression.

Page 21

  • Example 2 (Cont’d): evaluation leads to an 8- or 9-carbon chain; the correct parent is Nonane (a 9-carbon chain) in the illustrated solution.

Page 22

  • Example 2 (Cont’d): use the lowest numbering for substituents: numbers shown from 1 to 9 vs. a reversed set, choosing the set that yields the lowest set of locants.

Page 23

  • Substituents in Example 2: 3,7-dimethyl and 4-ethyl.

Page 24

  • Substituents arranged in alphabetical order, disregarding di- in dimethyl (i.e., Ethyl comes before dimethyl).
  • Complete name given: (4-Ethyl-3,7-dimethylnonane).

Page 25

  • 3C. How to Name Branched Alkyl Groups:
    • For alkanes with more than two carbon atoms, more than one derived alkyl group is possible.
    • Examples: Propyl, Isopropyl (or 1-methylethyl).

Page 26

  • Four-carbon groups: tert-butyl (or 1,1-dimethylethyl); sec-butyl (1-methylpropyl); Butyl family includes isobutyl.

Page 27

  • A neopentyl group is referenced (2,2-dimethylpropyl).
  • Neopentyl is also part of the branched-alkyl naming discussion.

Page 28

  • Example 1 (unspecified molecular structure in this page): indicates there is an illustrative example for naming.

Page 29

  • Example 1 (Cont’d) parts (a), (b), (c), (d) show different possible parent chain lengths (6-, 7-, 8-, 9-carbon chains) to determine the longest chain as parent.

Page 30

  • Example 1 (Cont’d): shows final selection of the longest chain and numbering for substituents to minimize locants.

Page 31

  • Example 1 (Cont’d): final substitution numbering (e.g., 4,5 or 5,6) is chosen based on the lowest locants; two alternative drawings show equivalent options, with one preferred by locant rules.

Page 32

  • Example 1 (Cont’d): substituents identified as isopropyl and tert-butyl; the final name is 4-tert-Butyl-2-methyl-1-heptene.

Page 33

  • Example 1 (Cont’d): substitutes arranged alphabetically (tert-Butyl before isopropyl when applying the “ignore di- for alphabetization” rule).
  • Final complete name: 5-tert-Butyl-4-isopropylnonane is shown earlier; note that the exact drawing in this page leads to 5-tert-Butyl-4-isopropylnonane in one part and 4-tert-Butyl-2-methyl-1-heptene in another depending on the chosen parent chain and presence of a double bond.

Page 34

  • Example 2 introduction (unlabeled structure): introduces a second example to apply the rules.

Page 35

  • Example 2 (Cont’d): determine the longest-chain parent; ends with 8-, 9-, or 10-carbon chain suggestions; toward choosing Decane as parent in the given example.

Page 36

  • Example 2 (Cont’d): two alternative depictions of the same naming problem; focuses on obtaining the correct substituent locants.

Page 37

  • Example 2 (Cont’d): final substitution numbering and substituents listed; shows the logic for choosing the lowest set of locants when multiple options exist.

Page 38

  • Example 2 (Cont’d): substituents identified as sec-butyl and neopentyl; which has precedence affects the final naming.

Page 39

  • Example 2 (Cont’d): due to precedence of sec-butyl over neopentyl, the complete name is 10,8,6,4,2-5 ext{-sec-Butyl-6-neopentyldecane} (illustrative ordering shown; the key is sec-butyl takes precedence and locants are chosen accordingly).

Page 40

  • 3D. How to Classify Hydrogen Atoms:
    • 1° (primary) hydrogens, 2° (secondary) hydrogens, 3° (tertiary) hydrogens.
    • Illustrates how different hydrogen environments are categorized on hydrocarbon frameworks.

Page 41

  • 3E. How to Name Alkyl Halides:
    • Halogens are treated as substituents (prefix position), not as the main functional group.
    • Halogen names: F → fluoro, Br → bromo, Cl → chloro, I → iodo.
    • Naming follows rules similar to alkyl substituents.

Page 42

  • 3E. Examples:
    • 1,2-Bromo-1-chlorobutane (structure illustrated).
    • 1,4-Dichloro-3-methylhexane (structure illustrated).

Page 43

  • 3F. How to Name Alcohols:
    • IUPAC substitutive nomenclature can include up to four features: locants, prefixes, parent, suffix.
    • Example: 4-Methyl-1-hexanol (or 4-Methylpentan-1-ol).

Page 44

  • Rules for naming alcohols:
    • Select the longest continuous carbon chain to which the hydroxyl (OH) is directly attached.
    • Change the name of the corresponding alkane by dropping the final -e and adding the suffix -ol.
    • Number the chain to give the carbon bearing the OH the lowest possible number; use this number as the locant for the OH.

Page 45

  • Examples:
    • 2-Propanol (isopropyl alcohol).
    • 4-Methyl-1-pentanol (or 4-Methylpentan-1-ol) – note that 2-Methyl-5-pentanol is NOT used here.
    • 1,2,3-Butanetriol (glycerol) with correct numbering for three OH groups.

Page 46

  • Example 4 introduction (structure shown): demonstrates naming with multiple OH groups and substituents.

Page 47

  • Example 4 (Cont’d): identify the longest chain that contains the OH group; if the chain containing OH is not the longest, select the longest that contains OH for naming.
  • Example shows Heptane as parent with OH substituent at position 7 to illustrate the rule.

Page 48

  • Example 4 (Cont’d): assign the lowest possible locant to the carbon bearing OH; display: OH at position 1 or 2 as appropriate to minimize the locant.

Page 49

  • Example 4 (Cont’d): final name for the example given as 2-Heptanol or other variant depending on chosen chain; illustrates prioritization of OH-bearing chain.
  • Substituents considered and named accordingly locally.

Page 50

  • 4. How to Name Cycloalkanes – 4A. Monocyclic Cycloalkanes:
    • For cycloalkanes with a single ring, attach the prefix cyclo- to the name of the ring (e.g., cyclopropane, cyclopentane).

Page 51

  • Substituted cycloalkanes: examples include isopropylcyclopropane, methylcyclobutane, tert-Butylcyclopentane.

Page 52

  • Example 1 for monocyclic systems:
    • 1-Ethyl-3-methylcyclopentane
    • 1-Ethyl-4-methylcyclopentane
    • 3-Ethyl-1-methylcyclopentane (not 3-Ethyl-1-methyl- cyclopentane in a misordered form)

Page 53

  • Example 2 for monocyclic systems:
    • 4-Bromo-2-ethyl-1-methylcyclohexane
    • 1-Bromo-3-ethyl-4-methylcyclohexane
    • Note on lowest substituent numbers: 1,2,4 is preferred over 1,3,4 when applicable.

Page 54

  • Example 3 for monocyclic systems:
    • 4-Ethyl-3-methylcyclohexene
    • 1-Ethyl-2-methylcyclohexan-4-ol (and related notations) – OH is present on cyclohexane ring/C=C contexts.
    • The guiding principle remains that the carbon bearing OH (if present) should have the lowest possible number when the ring contains an OH group.

Page 55

  • Cycloalkylalkanes: naming when a single ring is attached to a longer chain:
    • Example: 1-Cyclobutylpentane.
  • When more than one ring is attached to a single chain:
    • Example: 1,3-Dicyclohexylpropane.

Page 56

  • 4B. Bicyclic Cycloalkanes:
    • Bicycloalkanes are alkanes containing two fused or bridged rings.
    • Example principle: total number of carbons determines the base name; e.g., bicycloheptane for seven carbons.

Page 57

  • Bridgehead naming concept: describe relationships between bridge atoms.
  • Example: Bicyclo[2.2.1]heptane (two-carbon left bridge, two-carbon right bridge, one-carbon middle bridge).

Page 58

  • Other bicyclic examples:
    • 7-Methylbicyclo[4.3.0]nonane
    • 1-Isopropylbicyclo[2.2.2]octane

Page 59

  • 5. How to Name Alkenes & Cycloalkenes:
    • Rule 1: Select the longest chain that contains C=C as the parent and change the ending from -ane to -ene.

Page 60

  • Rule 2: Number the chain to include both carbons of the C=C, starting from the end nearer the C=C; the position of C=C is given by the first carbon of the C=C as the prefix (the locant for the -ene suffix may precede the parent name or be placed immediately before the suffix).

Page 61

  • Examples:
    • 1-Butene (not 3-Butene)
    • 2-Hexene (not 4-Hexene)

Page 62

  • Rule 3: Indicate the locations of substituent groups by the numbers of the attached carbon atoms.
  • Example: 2-Methyl-2-butene (not 3-Methyl-2-butene).

Page 63

  • Rule 3 (Cont’d): more examples: 2,5-Dimethyl-2-hexene and 2,5-Dimethyl-4-hexene; ensure proper locant placement.

Page 64

  • Rule 4: For cycloalkenes, number to give the C=C carbons as 1 and 2, and give substituents lower numbers at the first point of difference.

Page 65

  • Example 3,5-Dimethylcyclohexene vs 4,6-Dimethylcyclohexene; shows first-difference rule in action for cycloalkenes.

Page 66

  • Rule 5: Name compounds containing both a C=C and an alcohol group as alkenols (or cycloalkenols); give the alcohol-bearing carbon the lower number.
  • Example: 2-Methyl-2-cyclohexen-1-ol (or 2-Methylcyclohex-2-en-1-ol).

Page 67

  • Examples (Cont’d): 4-Methyl-3-penten-2-ol (or 4-Methylpent-3-en-2-ol).
  • OH group positioning is prioritized in the presence of C=C.

Page 68

  • Rule 6: Vinyl group and allyl group:
    • Vinyl group: ethenylcyclopropane (or vinylcyclopropane).
    • Allyl group: prop-2-en-1-yl.
    • Example: 3-(Prop-2-en-1-yl)cyclohexan-1-ol (or 3-allylcyclohexanol).

Page 69

  • Rule 7: Cis vs. Trans isomerism:
    • Cis: identical or substantial groups on the same side of the C=C.
    • Trans: identical or substantial groups on opposite sides of the C=C.
    • Examples: cis-1,2-dichloroethene and trans-1,2-dichloroethene.

Page 70

  • Visual examples illustrating cis/trans relationships (diagrammatic).

Page 71

  • Example (Cont’d): complete name formation from a labeled structure including stereochemistry considerations in some drawings.

Page 72

  • Example (Cont’d): final naming for a given structure with a tert-butyl substituent and other substituents on a heptene framework (illustrated as 4-tert-Butyl-2-methyl-1-heptene in the notes).

Page 73

  • 6. How to Name Alkynes:
    • Alkynes are named similarly to alkenes but end with -yne.
    • Example: 2-Heptyne (structure shown).

Page 74

  • Example (Cont’d): more complex alkynes such as 9-Bromo-7-iodo-6-isopropyl-8-methyl-3-decyne.

Page 75

  • OH group priority over C≡C:
    • When both OH and C≡C are present, OH takes precedence for naming order.
    • Example: 3-Butyn-1-ol (with OH given the lowest possible number position in the presence of a triple bond).
  • Another example: 2-Methyl-5-octyn-2-ol demonstrates the prioritization of OH over the alkyne in determining locants and substituent positions.