Nomenclature of alkylsubstituted cycloalkanes

If ring size ≥ ≥ >=\geq≥ chain length, parent = cycloalkane (named as an alkylcycloalkane)
If ring size < chain length, parent = alkane (named as a cycloalkylalkane)
CCCC1CC1
Parent is cyclopropane => propylcyclopropane
CCCCC1CC1
Parent is butane => 1-cyclopropylbutane
CCC(C)C1CC1
2-cyclopropylbutane
Remember: C atoms are either part a ring or part of a chain, not both.
1-ethyl-1-propylcyclobutane
Multiple substituents on a ring:
  • First substituent is number 1
  • Minimize the number of the 2 nd 2 nd  2^("nd ")2^{\text {nd }}2nd  substituent
  • Minimize the number of the 3 rd 3 rd  3^("rd ")3^{\text {rd }}3rd  substituent . . .
    CC[C@]1(Cl)CCC[C@@H](Cl)C[C@H]1ClSClRHClRHCl
Not:
CC[C@H]1CCCC(Cl)C[C@H]1ClSHClRHCl

or
CCC1CCCC(Cl)CC1(Cl)ClClClCl
2,4-dichloro-1-ethylcycloheptane
As a last resort, number according to alphabetical order
CC[C@H]1CCC[C@@H](CC)C(F)CC1SHRHF

not:
C=C1CC[C@H](CC)CC[C@@H]1CCRHSH
1,5-diethyl-2-fluorocycloheptane
(1 st st  ^("st "){ }^{\text {st }}st  substituent is ethyl, not fluoro)

Stereoisomerism

Two molecules are stereoisomers if they have identical bond connectivity but different 3D arrangements in space.
Example: cis-trans isomerism


trans-1,2-dimethylcyclopropane
CC(C)[C]1CCC[C@@H](Br)C1RHBr
trans-1-bromo-3-isopropylcyclohexane
CCCCC1CCC1C
cis-1-butyl-2-methylcyclobutane

RING STRAIN

Ring strain is the amount of extra energy in a ring beyond that of a hypothetical strain-free model of cycloalkanes. The strain-free model is based on Δ H ∘ Δ H ∘ DeltaH^(@)\Delta H^{\circ}ΔH∘ comb of linear alkanes, which have no constraints on their conformations.
Heat of combustion: Δ H ∘ Δ H ∘ DeltaH^(@)\Delta H^{\circ}ΔH∘ comb = = === heat given off by hydrocarbon + O 2 ⟶ CO 2 + H 2 O  hydrocarbon  + O 2 ⟶ CO 2 + H 2 O " hydrocarbon "+O_(2)longrightarrowCO_(2)+H_(2)O\text { hydrocarbon }+\mathrm{O}_{2} \longrightarrow \mathrm{CO}_{2}+\mathrm{H}_{2} \mathrm{O} hydrocarbon +O2⟶CO2+H2O
Alkanes Δ H ∘ comb ( kJ / mol ) Δ H ∘ comb  ( kJ / mol ) quad DeltaH^(@)_("comb ")(kJ//mol)\quad \Delta \mathrm{H}^{\circ}{ }_{\text {comb }}(\mathrm{kJ} / \mathrm{mol})ΔH∘comb (kJ/mol)
CCCCCC
− 2220.0 − 2876.1 − 3536.3 ⟩ diff = − 656.12 d diff = − 660.2 .26 average = − 658.6 − 2220.0 − 2876.1 − 3536.3  diff  = − 656.12 d  diff  = − 660.2 .26  average  = − 658.6 {:[-2220.0],[-2876.1],[-3536.3]:)" diff "=-656.12 d" diff "=-660.2.26" average "=-658.6\left.\begin{array}{c} -2220.0 \\ -2876.1 \\ -3536.3 \end{array}\right\rangle \text { diff }=-656.12 d \text { diff }=-660.2 .26 \text { average }=-658.6−2220.0−2876.1−3536.3⟩ diff =−656.12d diff =−660.2.26 average =−658.6
Strain-free model of cycloalkanes ( C n H 2 n ) : Δ H ∘ comb = − 658.6 × n C n H 2 n : Δ H ∘ comb  = − 658.6 × n (C_(n)H_(2n)):DeltaH^(@)_("comb ")=-658.6 xxn\left(\mathrm{C}_{\mathrm{n}} \mathrm{H}_{2 \mathrm{n}}\right): \Delta H^{\circ}{ }_{\text {comb }}=-658.6 \times \mathrm{n}(CnH2n):ΔH∘comb =−658.6×n
Strain-free model  Strain-free   model  (" Strain-free ")/(" model ")\frac{\text { Strain-free }}{\text { model }} Strain-free  model  Expt.
(" Strain-free ")/(" model ") Expt. | $\frac{\text { Strain-free }}{\text { model }}$ | | | Expt. | | | :---: | :--- | :--- | :--- | :--- |
Diff. = = ===
Ring strain
Diff. = Ring strain| Diff. $=$ | | :---: | | Ring strain |
Sources of ring strain:
  1. Angle strain (distortion from 109.5 ∘ 109.5 ∘ 109.5^(@)109.5^{\circ}109.5∘ ).
  2. Eclipsing atoms.
  3. Steric strain (atoms too close).
Strain-free model of cycloalkanes ( C n H 2 n ) : Δ H ∘ comb = − 658.6 × n C n H 2 n : Δ H ∘ comb  = − 658.6 × n (C_(n)H_(2n)):DeltaH^(@)_("comb ")=-658.6 xxn\left(\mathrm{C}_{\mathrm{n}} \mathrm{H}_{2 \mathrm{n}}\right): \Delta H^{\circ}{ }_{\text {comb }}=-658.6 \times \mathrm{n}(CnH2n):ΔH∘comb =−658.6×n

CCCC1CCCCC1Nc1ccccc1NH

(a)

(b)

(c)

(a)

(b)

(c)

(a)

(b)
[O-][O+]([O-])O[Na]O-O+O-ONa

(c)

How to draw cyclohexane chair conformations

3D convention

~in plane









Ring-flip equilibrium



McMurry Table 4.1. 1,3-Diaxial Interaction in Monosubstituted Cyclohexanes
1,2-Dimethylcyclohexane

Question from a previous exam

Show all four chair conformers of cis- and trans-1-isopropyl-3-methylcyclohexane. Label each conformer cis or trans. In addition, label each conformer with a number from 1 to 4 . This number represents the relative energy of the conformer: 1 means the lowest energy and 4 means the highest energy. (1,3-diaxial interactions from McMurry: methyl 3.8 kJ / mol 3.8 kJ / mol 3.8kJ//mol3.8 \mathrm{~kJ} / \mathrm{mol}3.8 kJ/mol, isopropyl 4.6 kJ / mol 4.6 kJ / mol 4.6kJ//mol4.6 \mathrm{~kJ} / \mathrm{mol}4.6 kJ/mol.) Do not write energy values for molecules.
CC1CCC[C](C(C)C)C1
cis
CC(C)[C@H]1CCC[C@@H](C)C1SHRH
trans
diaxial:
Me-H
iPr-H
iPr-Me
cis
4
0 diax
0 gauche
1
Bicyclic molecules (will not be on exam 1)