Robert B. Grossman. University . of . Kentucky. Professor of Chemistry. Synthetic. . Organic Chemistry. 1987. B.A., Princeton University. 1992. Ph. D., Massachusetts Institute of Technology. 1992-1994.
In general, we look at what occurs and try to learn how it happens. Common patterns describe the changes. Addition reactions – two molecules . combine. Elimination reactions – one molecule splits into two.
Types of Reactions. Types of Reactions. There are . 9. . main types of reactions we will examine:. Combustion. Substitution. Addition. Halogenation. , . Hydrogenation, . Hydrohalogenation. , Hydration.
Reactions. Reactions. Hydrolysis of a polysaccharide. polysaccharide + water . → . disaccharide. Example:. 2(C. 6. H. 10. O. 5. ). n. + . n. H. 2. O . →. . n. C. 12. H. 22. O. 11. Hydrolysis of a disaccharide.
Chemistry Department, College of Science, King Saud University. http://fac.ksu.edu.sa/melnewehy. Organic Halogen Compounds. Classes and Nomenclature of Halogen Compounds. - Alkyl halides. , . R-X.. - Depending on the type of carbon to which the halogen is attached, .
. . . Dr. . Oruba. . . lec.3 . 1. Microbial Metabolism. . . It’s the . growth, nutrition, . And. metabolism . OF BACTERIA. What does physiology means ?. Metabolism. Metabolism:. Is the sum of all chemical reactions in the body. .
ALkanes. Chapter 10.2:. Structure, bonding and chemical reactions involving functional group inter-conversions are key strands in organic chemistry. Chapter 20.1:. Key organic reaction types include nucleophilic substitution, electrophilic addition, electrophilic substitution, and redox reactions. Reaction mechanisms vary and help in understanding the different types of reactions taking place..
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Presentation on theme: "Organic REACTIONS:"— Presentation transcript:
Organic REACTIONS: ALkanes
Structure, bonding and chemical reactions involving functional group inter-conversions are key strands in organic chemistry
Key organic reaction types include nucleophilic substitution, electrophilic addition, electrophilic substitution, and redox reactions. Reaction mechanisms vary and help in understanding the different types of reactions taking place.Slide2
hydrocarbons where carbons in the chain are singly bonded to one another
: relatively low
Carbon-hydrogen bond relatively strong (relatively high bond energy)
slightly polar (electronegativity difference of
RXN types are
: rapid, exothermic oxidation of combustible
2: Substitution: two main types
FRCR: free radical chain reaction
Combustion: rapid, exothermic oxidation of combustible materials.
Most common alkane RXN
fuel source (alkane)source of ignition (required to reach activation energy)
Complete combustion of hydrocarbons produces CO
2OAll carbon converts to CO2 and all Hydrogen converts to H2O. When balancing:
# of C in the alkane = # CO2
molecules produced # of H in the alkane = 2 X H2
O molecules produced
In most situations, combustion of hydrocarbons is incomplete because of insufficient oxygen. Products of incomplete combustion are responsible for a large amount of urban pollution: carbon monoxide (CO) carbon (soot)
Burning other hydrocarbons (unsaturated) is very similar
ArenesThe more unsaturation (higher C:H ratio) the higher the smokiness due to unburned carbon
2 and H2O are greenhouse gases = absorb radiation and increase heat average world temp
CO toxin as binds irreversibly to hemoglobin in blood
C (soot) causes respiratory distress and contributes to smog and global dimmingAlkanes: CombustionSlide6
Free radical chain reaction:
alkane RXT with halogen = halogenoalkanes
One Hydrogen (H) in
the alkane is replaced by a
halogen (X) reaction of ethane with chlorine:
-CH3(g) + Cl
) CH3-CH2-Cl(g) +
Ethane chlorine chloroethane hydrogen chloride
Alkanes-Substitution RXNs: FRCRSlide7
brought about by exposure to
high temps (provides energy of activation)Chloroethane can RXT with more Cl2
Cl2 eventually convert to hexachloroethane (substitute all H with Cl)
Alkanes-Substitution RXNs: FRCRSlide8
any molecule or atom with a single unpaired electron
highly reactive Reaction proceeds in 3 distinct phases. RXN of CH4 with Cl2
example:Initiation: free radicals are produced
Propagation: products are formed and radicals are reformedTermination: radicals are used up
Alkanes-Substitution RXNs: FRCRSlide9
1. Initiation phase:
UV light) can break covalent bond between the 2 Cl atomsReleasing unpaired Cl atoms (free radicals)
homolytic fission: each atom results in one e- (“equal
Therefore, heterolytic fission is unequal splitting both electrons result with one atomLarge reduction in stability for
Alkanes-Substitution RXNs: FRCRSlide10
Unstable Cl• readily forms
new covalent bond with whatever is
Here, H atom from CH4 Cl radical pulls H atom
(including its e- which is currently
shared with carbon atom) off of CH
This forms HCl and free radical, •CH3CH3• will then pull a
2 molecule, reforming a chlorine radical. Continues in a chain reaction.
Alkanes-Substitution RXNs: FRCRSlide11
occurs when all of the radicals are consumed.
radicals can combine with each other to form a molecule of Cl2OR they can combine with
to form CH3Cl
OR 2 methyl
radicals can combine to form ethaneSince ethane found to be produced during the halogenations of methaneMechanism for
is indeed the one illustrated in the
diagram.. So we know it’s good!
Alkanes-Substitution RXNs: FRCRSlide12
bromine were used instead of
brown color provides simple visual method to monitor the progress of the reactionAs
the brown colored bromine is consumed, the color would gradually fade
Note: reaction is not
in the darkThere is no source of energy to create the necessary radicalsAlkanes-Substitution RXNs: FRCRSlide13
Nucleophilic substitution of
Nucleophile is e- rich and attack areas of e- deficiency
Nucleophile can be anything with a lone pair of electrons, but common examples are:Hydroxide ion:OH-Ammonia: NH
CN-Electrophile is e- deficient and accepts e- pairs from a nucleophileElectrophile