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(c) doc b(c) doc bDoc Brown's Chemistry  Revising Advanced Level Organic Chemistry

Revision Notes PART 3 HALOGENOALKANES (haloalkanes, alkyl halides)

3.1 The molecular structure and naming-nomenclature of halogenoalkanes once known as 'haloalkanes' ('alkyl halides') - 3.1.1 The homologous series of HALOGENOALKANES

of general formula CnH2n+1X (X = F, Cl, Br or I, initially n = 1, 2 or 3)

How do we name haloalkanes? What is the molecular structure of halogenoalkanes? This page describes the molecular structure and how to name halogenoalkanes of the simplest monosubstituted halogenoalkanes and some polysubstituted haloalkanes of the C1, C2 and C3 carbon chains. Examples of displayed formula of halogenoalkane molecules (fluoro, chloro, bromo and iodo alkane derivatives), graphic formula, molecular formula, skeletal formula, structural formula of these homologous series, including isomers of halogenoalkane molecules and some of the further halogen substitution products including CFCs, HFCs and HCFCs. Some 'old' trivial and commercial names of the fluoroalkanes, chloroalkanes, bromoalkanes, and iodoalkanes are quoted in () though their use should be avoided if possible.

See also 3.1.2 more haloalkanes of C4 * 3.1.3 more haloalkanes >C4_and cyclohaloalkanes


A brief guide to halogenoalkane nomenclature

  • The generic suffix name (..ane) is based on the longest carbon chain. 1 carbon, methane; 2 carbons, ethane; 3 carbons, propane; 4 carbons, butane. After these 4 preserved 'old trivial' names, the name is 'numerically' systematic eg 5 carbons, pentane; 6 hexane, 7 heptane etc.
  • The halogenoalkane structures are based on replacing one or more hydrogen atoms in the alkane structure with a halogen atom X (X = F, Cl, Br or I).
  • The positions of the substituent(s), denoted with a prefix eg halo… or alkyl… groups, are denoted by using the lowest possible numbers for the associated carbon atoms in the main chain.
  • If there is more than one 'type' of substituent eg using the prefixes: bromo…, chloro…, methyl… etc., they are written out in alphabetical order irrespective of carbon atom number (note: di, tri are ignored in using this rule).
  • The examples on this page are based on 1 to 3 carbon atoms
  • Some 'old' and commercial names are quoted in () though their use should be avoided if possible [but many still used - just put one into GOGGLE!].
  • A sub-CLASSIFICATION based on structural differences, which can have chemical consequences on e.g. rate of reaction or products formed in a reaction.
    • Halogenoalkanes are classified according to the atoms/groups attached to the carbon of the halogen atom X.
    • Primary halogenoalkanes have the structure R-CH2-X, R = H, alkyl, aryl etc. i.e. apart from chloromethane they have one alkyl/aryl group attached to the C of the C-X group.
      • e.g. chloroethane CH3CH2Cl
    • Secondary halogenoalkanes have the structure R2CH-X, R = alkyl or aryl etc. i.e. they have two alkyl/aryl groups attached to the C of the C-X group.
      • e.g. 2-bromobutane CH3CHBrCH2CH3 
    • Tertiary halogenoalkanes have the structure R3C-X, R = alkyl or aryl etc. i.e. they have three alkyl/aryl groups attached to the C of the C-X group.
      • e.g. 2-iodo-2-methylpropane (CH3)3CI
  • NOTE: Some 'old' and commercial names are quoted in () though their use should be avoided if possible.
  • AND some abbreviations:
    • CFC = chlorofluorocarbon (molecule consists of C, Cl, F atoms)
    • HFC = hydrofluorocarbon (molecule consists of C, H, F atoms)
    • HCFC = hydrochlorofluorocarbon (molecule consists of C, H, Cl, F atoms)
  • The shapes and bond angles of simple molecules - section on bond angles in organic molecules

    • Virtually all the bond angles for the molecules on this page are ~109o e.g. the H-C-H, H-C-Cl, H-C-Br, Cl-C-F etc. bond angles will be ~109o


Examples of non-cyclo C1-3 HALOGENOALKANES

1. The simplest halogenoalkane is exemplified by chloromethane (methyl chloride), whose formula and structured are shown in 4 styles. (a)(c) doc bmolecular formula, (b)(c) doc b abbreviated structural formula,

(c)(c) doc b, full structural formula, (d)(c) doc b '3D' representation of the structural formula. The H-C-H and H-C-Cl bond angles will be ~109o

 

2. to 7. Are examples of multi-substituted halogenoalkanes based on methane …

(c) doc b 2. (a) trichlorofluoromethane, (CFC-11, a chlorofluorocarbon or CFC).The Cl-C-Cl and F-C-Cl bond angles will be ~109o

(b)(c) doc b, chlorotrifluoromethane (a CFC)

 

3. (c) doc b (a) dichlorodifluoromethane, (CFC-12),

(b)(c) doc b, dichlorofluoromethane (a HCFC)

 

4. (c) doc bdifluoromethane (a hydrofluorocarbon or HFC, methylene difluoride)

5. (c) doc btribromomethane

6. (c) doc btetrachloromethane, (carbon tetrachloride)

7. (c) doc bchlorodifluoromethane, (HCFC-22 a hydrochlorofluorocarbon or HCFC)

 

8. Bromoethane (ethyl bromide) exemplifies the simplest mono-substituted alkane with 2 carbon atoms.

(a)(c) doc b molecular formula, (b)(c) doc b abbreviated structural formula,

(c)(c) doc b more expanded structural formula, (d)(c) doc b full graphic structural formula. The H-C-H and H-C-Br bond angles will be ~109o

(e)(c) doc b '3D' structural formula, (f)(c) doc b skeletal formula

 

9. to 14., show a series of multi-substituted halogenoethane molecules (with the possibility of positional isomerism with only 2 carbon atoms) ...

9. (a) (c) doc b, 1-chloro-1,1,2-trifluoroethane, (b) (c) doc b2-chloro-1,1,1-trifluoromethane (a HCFC), (c) (c) doc b, 1-chloro-1,2-difluoroethane, (d) (c) doc b, 2-chloro-1,1-difluoroethane, (e) (c) doc b, 1-chloro-1,2,2-trifluoroethane

 

10. (a) (c) doc b, 1-chloro-1-fluoroethane, (b) (c) doc b, 1-chloro-2-fluoroethane, (c) (c) doc b, 1-chloro-1,1-difluoroethane, (d) (c) doc b, 1,1,2-trichloro-1,2,2-trifluoroethane (CFC-113)

 

11. (c) doc b2,2-dichloro-1,1,1-trifluoroethane (HCFC-123)

 

12. (a) (c) doc b, 1,1-difluoroethane (HFC-152a), (b) (c) doc b, 1,2-difluoroethane

 

13. (a) (c) doc b, 1,1-dichloro-1-fluoroethane (HCFC-141b), (b) (c) doc b, 1,1-dichloro-2,2-difluoroethane

 

14.(a)(c) doc b 1,1,1-trifluoroethane, (b) (c) doc b, 1,1,2-trifluoroethane, (c) (c) doc b1,1,1,2-tetrafluoroethane (HFC-134a), (d) (c) doc b, 1,1,2,2-tetrafluoroethane

 

with 3 carbon atoms you get positional isomerism with only 1 halogen atom (1- or 2- …)

15. (a)(c) doc b, (b)(c) doc b , (c)(c) doc b, 1-bromopropane (propyl bromide)

 

16. (a)(c) doc b, (b)(c) doc b, (c) (c) doc b, (d)(c) doc b, 2-bromopropane (isopropyl bromide)

 

17.(a)(c) doc b, (b)(c) doc b, (c)(c) doc b , 2-chloropropane (isopropyl chloride)

18.(a)(c) doc b, (b)(c) doc b, (c)(c) doc b, (d)(c) doc b , 1-iodopropane (propyl iodide)

 

19. (c) doc bWith 2 like halogen atoms there are four positional isomers

(a)(c) doc b , (c) doc b, (c) doc b, 1,1-dichloropropane

(b)(c) doc b , (c) doc b, (c) doc b, 1,2-dichloropropane

(c)(c) doc b  , (c) doc b, (c) doc b, 1,3-dichloropropane

(d)(c) doc b  , (c) doc b, (c) doc b, 2,2-dichloropropane

 

20.(c) doc b  with 3 like halogen atoms there are 5 positional isomers

(a)(c) doc b , (c) doc b, (c) doc b, 1,1,1-trifluoropropane

(b)(c) doc b , (c) doc b, (c) doc b, 1,1,2-trifluoropropane

(c)(c) doc b , (c) doc b, (c) doc b, 1,1,3-trifluoropropane

(d)(c) doc b , (c) doc b, (c) doc b, 1,2,2-trifluoropropane

(e)(c) doc b , (c) doc b, (c) doc b, 1,2,3-trifluoropropane


See also 3.1.2 more haloalkanes of C4 * 3.1.3 more haloalkanes >C4_and cyclohaloalkanes



Revision notes for GCE Advanced Subsidiary Level AS Advanced Level A2 IB Revise AQA GCE Chemistry OCR GCE Chemistry Edexcel GCE Chemistry Salters Chemistry CIE Chemistry, WJEC GCE AS A2 Chemistry, CCEA/CEA GCE AS A2 Chemistry revising courses for pre-university students (equal to US grade 11 and grade 12 and AP Honours/honors level courses)

formulae keywords: how to name naming nomenclature empirical molecular formula graphic formula displayed formula skeletal formula structural isomers isomerism  haloalkanes halogenoalkanes alkyl halides chloroalkanes bromoalkanes iodoalkanes fluoro alkanes CFC HFC HCFC CFCs HFCs HCFCs CH3Cl CCl3F CCl2F2 CH2F2 CHBr3 CCl4 CHClF2 C2H5Br CH3CH2Br CH3-CH2 -Br CH2FCClF2 CF3CH2Cl CHCl FCH2F CH2F2CH2Cl CHF2CHClF CH3CHClF CH2ClCH2F CH3CClF2 CCl2FCClF2 CF3CHCl2 CH3CHF2 CH3CCl2F CH3CF3 CH2FCHF2 CH2FCF3 CHF2CHF2 C3H7Br CH3CH2CH2Br CH3-CH2-CH2-Br CH3CHClCH3 C3H7I CH3CH2CH2Br CH3-CH2-CH2-Br CH3CHBRCH3 CH3CHClCH3 C3H7I CH3-CH2-CH2-I CH3CH2CH2I C3H6Cl2 C3H6F3

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