Chemistry of Cycloalkane (prayatna.kunj@gamil.com).pptx

Submitted By:
Mr. Prayatna Kunj.
PharmD 1st Year.
Under The Supervision Of:
Dr. Rahul Kumar Maurya.
Faculty of Pharmacy.
Amity Institute of Pharmacy.
Amity University , Lucknow.
prayatna.kunj@gamil.com

• 1. Introduction
• 2. Physical properties
• 3. Prepration
• 4. Baeyer’s strain theory
• 5. Orbital picture of angle strain
Cyclooctane
Cycloalkane
Content

1. Introduction:-
3
• They are saturated hydrocarbon in
which the carbon atom joined by
single covalent bond to form a ring
• They are also called cycloparaffins
and salicylic compound
• Hybridization - sp³ hybridization
• IUPAC(Nomenclature) - Same as
alkanes, but use cycle as prefix
Example:-

2. Physical property of Cycloalkane
1.Cyclopropane. -32.8 -127.4
2.Cyclobutane. 12.5 -90.7
3.Cyclopentane. 49.5 -13.9
• Cyclopropane and Cyclobutane are gases at room temperature , remaining
are liquids.
• Cycloalkane are insoluble in water but dissolve in ethanol and ether.
• Melting and boiling points of cycloalkane shows a gradual increase with the
increase in molecular weight.
• Example:- Boiling point(⁰C) Melting point(⁰C)

* Chemical Reaction of Cycloalkane
• Cycloalkane gives two reaction:-
(i) Substitution Reaction
(ii) Addition reaction (open ring reaction)
(i) Substitution Reaction:- In this reaction ,one hydrogen atom replaced, but ring does
not affected.
—#substitute with or
UV light, it gives substitute products.
(a) When cyclopropane react with chlorine in the presence of uv light, it gives
chlorocyclopropane.

(b) when cyclohexane react with chlorine in the presence of UV light , it gives
chlorocyclohexene.
Eg.
Eg.

(ii) Addition Reaction(ring opening reaction):- In this reaction, bond will break and the
ring will open.
-Higher cycloalkane does not give reaction.
-#addition of &
(a)When cyclopropane react with bromine( ) in the dark to give 1,3 dibromopropane
( used as a solvents ).
-#Addition of
(b)cyclopropane react with in the presence of Ni(Nickel) at 80⁰ C it give propane.
Cyclopropane Propane

3.Method of Preparation of Cycloalkane
Types
1. From Dihalide
2. Dieckmann reaction
3. Simmons-smith reaction
4.From aromatic hydrocarbons
5. From calcium salt of dicarboxylic acid

1. From Dihalide:-
-Terminal dihalide when treated with sodium(Na) or Zinc(Zc) from cycloalkanes.
(1,3 dibromopropane) (Cyclopropane)
2. Dieckmann reaction(from ester of dicarboxylic acid):-
-Ester of dicarboxylic acid, when heated with sodium,β-ketoester is formed,
which further on hydrolysis give cyclic ketones, which on dimension reduction
give cycloalkane.
Eg.1.
Eg.2.

Eg 1.
3. Simmons-smith reaction(from alkenes):-
-When alkene are treated with methylene iodine( ) in the presence of a
zinc-copper(Zn-Cu) couple, cyclopropane derivatives are formed.
Eg.1
Eg.2

4. From aromatic hydrocarbons
-Six membered cycloalkane can be prepared by the catalyst reduction of
benzene and its derivatives.
Pressure
Eg.1
5. From calcium salts of dicarboxylic acids
-When the calcium barium salts of dicarboxylic acids are heated, cyclic
ketones are formed, then further on dimension reduction cyclic ketone
converts into cycloalkanes.
Eg.1
Cyclic ketone

4. Baeyer’s Strain theory
Intro:-
• Adolf Baeyer proposed in 1885,and he get noble prize for this theory in1905.
• He explain the relative stability of starting few cycloalkane.
• His theory is based on the fact that, the normal angle between pair of carbon atom is
109⁰28’.
• Now , he assumed that all cycloalkane are planar.
• Stability of cycloalkane depends upon angle strain.
• In cycloalkane = more the angle strain , the more unstable.
Angle strain ⬆️ = Stability ⬇️

Angle strain = It is angle difference between desired angle (109⁰28’) and actual angle
Angle strain = 1/2 [ desired angle - actual angle ]
= 1/2 [ 109⁰28’ - Actual angle ]
Eg.(i) Cyclopropane
Desired angle = 109°28'
Actual strain = 60°
Ange strain=24.75

Eg.2 Cyclobutane
Angle strain= 1/2 [ 109°28'- 90° ]
= 9°44'
Eg.3 Cycle pentane
Desired angle strain=109°28'
Actual angle strain=90°
Angle strain=1/2[109°28'-108°]
= 0.44'
Eg.4 Cycle hexane
Angle strain=1/2[109°-120°]
=-5°16'

According to Baeyer’s strain theory:-
*Stability of cycloalkane are :-
— cyclopropane<cyclobutane<cyclohexane<cyclopentane
Stability
Limitation :—
- This theory only applies on the lower cycloalkane,bayers was not able to explain the effect of angle strain in layer ring system.
-According to baeyer cyclopentane should be much stable than cyclohexane ,
but practically it is reversed.(cyclohexane is more stable than cyclopentane)
-So, higher cycloalkane are not follow this rule(cyclohexane,cycloheptane are more stable)
-They do not give ring opening reaction like cyclopropane.

5. Orbital Picture Of Angle Strain
—Bent Bond / - Banana bond theory
* Concept of maximum overlap of carbon orbitals.
* It is also called as banana bond theory , because bond look like as a banana shape.
* This theory also explain the stability of cycloalkanes( why cyclopropane most unstable).
* It is based on that , Greater the overlapping of atomic orbital stronger is the bond.
* Stronger is the bond ⬆️ = stability ⬆️.
Eg.
Sigma bond = stronger(due to good overlapping)
Pi bond = weaker(due to bad overlapping)

* But in cyclopropane bent bond is formed, which is intermediate between sigma and pi bond.
(stronger from pi bond and weaker than sigma bond)
Sp³
Hybridisation
s=25%
p=75%
s=16%
p=84%
*Cyclopropane:—
- due to formation of bent bond, the cyclopropane c-c bond is
weaker than normal c-c sigma bond.
- so, due to weaker bond cyclopropane is unstable and it can give
ring opening reaction easily.
- The cyclopropane , c-c-c bond angle is decreased slightly from
109°28' to 104°.

- The decrease in overlap result in weakening of the bond and therefore
partially explain the instability of cyclopropane.
* Bent bond is formed in cyclopropane , due to their less angle(60°) than
109°28'
-Cyclobutane is more stable than cyclopropane but less than cyclopentane.
*Sachse-Mohr theory (theory of stainless rings):-
- Sachse and Mohr proposed this theory in 1918 to explain about the stability of
cyclohexane and higher cycloalkane .
- according to Baeyer’s member higher than cyclopentane should be increasingly
unstable ( limitation ).
- But according to Sachse-Mohr :-
*Cycloalkane are not in a plane ( co-planar ).
- Sachse Mohr’s theory proposed that higher membrane ring can free from strain if all
the ring carbon are not found into one plane. prayatna.kunj@gamil.com

- They exhibit in two non-planar ‘folded’ or ‘puckered’ conformation both of which
are completely free from strain.
- These are stainless as the carbon atom lie in different planes and the normal angle
(109°28') is retained.
Example:- Cyclohexane
- chair form is more stable than boat form(chair form two types positions):—
(i) Axial position— perpendicular to the plane of the ring.
(ii) Equatorial position — around the plane of the ring

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