ORGANIC COMPOUNDS : ALKANES Chemistry 21A Dr. Dragan Marinkovic Urea was first discovered in human urine by H.M. Rouelle in 1773 It was synthesized in

ORGANIC COMPOUNDS: ALKANES

Chemistry 21A Dr. Dragan Marinkovic

Urea was first discovered in human urine by H.M. Rouelle in 1773

It was synthesized in 1828 by Friedrich Wöhler and was the first organic compound to be synthesized from inorganic starting materials

This discovery prompted Wöhler to write triumphantly to Berzelius:-"I must tell you that I can make urea without the use of kidneys, either man or dog. Ammonium cyanate is urea."

Friedrich Wöhler, who prepared it from

silver isocyanate through a reaction with ammonium chloride

AgNCO + NH4Cl → (NH2)2CO + AgCl

Although Wöhler was attempting to prepare ammonium cyanate, by forming urea, he inadvertently discredited VITALIZM, the theory that the chemicals of living organisms are fundamentally different from inanimate matter,

thus starting the discipline of ORGANIC CHEMISTRY.

NH4NCO → (NH2)2CO



An ORGANIC COMPOUND is any member of a large class of chemical compounds whose molecules contain carbon.

The name "ORGANIC" is historical, dating back to the 19th century, when it was believed that organic compounds could only be synthesized in living organisms through VIS VITALIS - the "life-force".

ORGANIC CHEMISTRY

the study of carbon containing compounds.

INORGANIC CHEMISTRY

the study of the elements and noncarbon compounds.

Inorganic exceptions:CO, CO2, carbonates, bicarbonates, cyanides, cyanates, isocyanates

Na2CO3 NaHCO3 NaCN NaCNO NaNCO



Characteristics of organic substances

ORGANIC COMPOUNDS are generally covalently bonded.

This allows for unique structures such as long carbon chains and rings.

Carbon atoms form very stable covalent bonds with one another (catenation). In contrast to inorganic materials, organic compounds typically melt, boil, sublimate, or decompose below 300°C.

Neutral organic compounds tend to be less soluble in water compared to many inorganic salts, with the exception of certain compounds such as low molecular weight alcohols and carboxylic acids where hydrogen bonding occurs.



Characteristics of organic substances

Organic compounds tend rather to dissolve in organic solvents which are either pure substances like ether or ethyl alcohol, or mixtures, such as the paraffinic solvents such as the various petroleum.

Like inorganic salts, organic compounds may also form crystals.

Unique property of carbon in organic compounds is that its valency does not always have to be taken up by atoms of other elements, and when it is not, a condition termed unstauration results. In such cases we talk about

carbon carbon DOUBLE BONDS or TRIPLE BONDS.

Double bonds alternating with single in a chain are called CONJUGATED DOUBLE BONDS.

An aromatic structure is a special case in which the conjugated chain is a closed ring.



Carbon compoundsLife as we know it is carbon based. This means that most of the compounds you are made of contain the element carbon. You use carbon compounds every day.

Plastic, rubber, and gasoline, clothing, markers, tennis rackets, are carbon compounds. Everything in house that is not metal, ceramic or glass is organic/carbon material.In fact, there are over 12 million known pure carbon compounds (and imagine all possible mixtures)!



A carbon atom can form chemical bondswith other carbon atoms in long chainsCarbon is unique among the elements.or rings.Some carbon compounds contain several thousand carbon atoms.

The carbon compounds in livingthings are classified into four groups:

1. CARBOHYDRATES

2. LIPIDS

3. PROTEINS

4. NUCLEIC ACIDS

glucose in cells CARBOHYDRATES

cell membrane - LIPIDS

hair - PROTEIN

fat layer underneath skin - LIPIDS

nucleus of cell – nucleic acids (DNA)



Property Organic Inorganic

Bonding covalent ionic or covalent

Forces between molecules

generally weak quite strong

Number of compounds

6 million+ around 250,000

Standard state low melting solid, liquid, or gas

solid

Water solubilty mostly insoluble mostly soluble

Organic solubilty mostly soluble mostly insoluble

Color majority colorless often colored

Conductibility nonconductorsconductors in molten or aqueous state

Combustibility often flammable very few burn

Rate of reactions slow fast

COMPOUNDS



We assume that the single 2s, and the three 2p orbitals of carbon mix into four sp3 hybrid orbitals which are chemically and geometrically identical; the latter condition implies that the four hybrid orbitals extend toward the corners of a tetrahedron centered on the carbon atom.

In the ground state of the free carbon atom, there are two unpaired electrons in separate 2p orbitals. In order to form four bonds (tetravalence), need four unpaired electrons in four separate but equivalent orbitals.





Methane is the simplest hydrocarbon; the molecule is approximately spherical, as is shown in the space-filling model:

In the ammonia molecule, for example, the nitrogen atom normally has three unpaired p electrons, but by mixing the 2s and 3p orbitals, we can create four sp3-hybrid orbitals just as in carbon. Three of these can form shared-electron bonds with hydrogen, resulting in ammonia, NH3. The fourth of the sp3 hybrid orbitals contains the two remaining outer-shell electrons of nitrogen which form a non-bonding lone pair. In acidic solutions these can coordinate with a hydrogen ion, forming the ammonium ion NH4

+.



OXYGENWATER



By replacing one or more of the hydrogen atoms in CH4 with another sp3 hybridized carbon fragments, hydrocarbon chains of any degree of complexity can be built up. The simplest of these is ethane:



HYDROCARBONS

SATURATED UNSATURATED

ALKANES ALKENES ALKYNES

AROMATICS

H

H

H

H

H

H C C

H

HH

H

CC

HH CC

H

H

H

H

H

HC

C

CC

CC

RING WITH CONJUGATED DOUBLE BONDS

CONJUGATED DOUBLE BONDS

ISOLATED DOUBLE BONDS

PARAFFINS

CYCLOALKANES



Structural isomerism, or constitutional isomerism, is a form of isomerism in which molecules with the same molecular formula have atoms bonded together in different orders

ISOMERS (Greek isos = "equal", méros = "part") are compounds with the same molecular formula but different structural formula

A simple example of isomerism is given by propane: it has the formula C3H8O (or C3H7OH) and occurs as two isomers: propan-1-ol (n-propyl alcohol; I) and propan-2-ol (isopropyl alcohol; II)

propan-1-ol (n-propyl alcohol) propan-2-ol (isopropyl alcohol) ethyl methyl ether

C3H8O



Example of skeletal isomerism

isopentane (2-methylbutane)

n-pentane

pentan-2-ol pentan-3-ol

position isomerism

functional group isomerism

C6H12

CH3

OCH2

CH

2

CH3 CH3

CH

2

OCH

2

CH3

This type of isomerism is due to the unequal distribution of carbon atoms on either side of functional group. METAMERISM belongs to same homologous series.

methyl propyl etherdiethyl ether

1-hexene cyclohexane

C5H12C5H12O

C4H10O



FUNCTIONAL GROUPS

are specific groups of atoms within molecules that are responsible for thecharacteristic chemical reactions ofthose molecules. The same functional group will undergo the same or similar chemical reaction(s)regardless of the size of the moleculeit is a part of. However, its relative reactivity can bemodified by nearby functional groups.

ethane ethene (ethylene)

ethyne (acethylene)

Ether(ethyl ether)

(diethyl ether)

Cumene(isopropyl benzene)methanol

(methyl alcohol)



FUNCTIONAL GROUPS

are specific groups of atoms within molecules that are responsible for thecharacteristic chemical reactions ofthose molecules. The same functional group will undergo the same or similar chemical reaction(s) regardless of the size of the molecule it is a part of. However, its relative reactivity can bemodified by nearby functional groups.

methyl ethyl ketone(butanone)

acetaldehyde(ethanal)

acetic acid(ethanoic acid)

acetamidemethylamine ethyl butyrate(ethyl butanoate)

O.

.

C

carbonylgroup



HYDROCARBONS

SATURATED UNSATURATED

ALKANES ALKENES ALKYNES

AROMATICS

H

H

H

H

H

H C C

H

HH

H

CC

HH CC

H

H

H

H

H

HC

C

CC

CC

RING WITH CONJUGATED DOUBLE BONDS

CONJUGATED DOUBLE BONDS

ISOLATED DOUBLE BONDS

PARAFFINS

CYCLOALKANES



Petroleum (L. petroleum, from Greek πετρέλαιον, lit. "rock oil") or crude oil is a naturally occurring, flammable liquid found in rock formations in the Earth consisting of a complex mixture of hydrocarbons of various molecular weights, plus other organic compounds.

Four different types of hydrocarbon molecules appear in crude oil. The relative percentage of each varies from oil to oil, determining the properties of each oil

Composition by weight

Hydrocarbon Average Range

Alkanes 30% 15 to 60%

Cycloalkanes 49% 30 to 60%

Aromatics 15% 3 to 30%

Asphaltics 6% remainder



NameMolecularFormula

StructuralFormula

Iso-mers Name

MolecularFormula

StructuralFormula

Isomers

methane CH4 CH4 1 hexane C6H14 CH3(CH2)4CH3 5

ethane C2H6 CH3CH3 1 heptane C7H16 CH3(CH2)5CH3 9

propane C3H8 CH3CH2CH3 1 octane C8H18 CH3(CH2)6CH3 18

butane C4H10 CH3CH2CH2CH3 2 nonane C9H20 CH3(CH2)7CH3 35

pentane C5H12 CH3(CH2)3CH3 3 decane C10H22 CH3(CH2)8CH3 75

ALKANES ≡ PARAFFINS

Group CH3– C2H5– CH3CH2CH2– (CH3)2CH– CH3CH2CH2CH2–

Name Methyl

Ethyl Propyl Isopropyl Butyl

Latin parum (= barely) + affinis with the meaning here of "lacking affinity"

Alkyl



methane CH4 CH4 1 hexane C6H14 CH3(CH2)4CH3 5

ethane C2H6 CH3CH3 1 heptane C7H16 CH3(CH2)5CH3 9

propane C3H8 CH3CH2CH3 1 octane C8H18 CH3(CH2)6CH3 18

butane C4H10 CH3CH2CH2CH3 2 nonane C9H20 CH3(CH2)7CH3 35

pentane C5H12 CH3(CH2)3CH3 3 decane C10H22 CH3(CH2)8CH3 75


Name Methyl


Alkyl

THE ALPHABET OF ORGANIC CHEMISTRY



General formula for alkanes:



Nowadays, the main source of methane is "Natural Gas", which originates in the same way as crude oil, by the anaerobic decomposition of microscopic sea animals under the pressure of layers of silt and mud over a period of millions of years. This can also occur in swamps and marshes, when plant matter decays ("marsh gas"), and in landfill sites; in digesters breaking down sewage sludge; and by enteric fermentation in livestock (e.g. ruminants such as cattle and sheep), as well as being formed when termites digest the cellulose in the wood they have eaten.

Cows and other ruminants have methanogenic bacteria in their rumen which can turn digested carbon compounds into methane, emitted as flatus, some 200-300 litres of gas a day. Most of the flatus is nitrogen, but cases have been reported of cows' flatus being ignited, though not explosively.

anaerobicin absence of air (oxygen)



The alkanes from pentane (C5H12) to octane (C8H18)

are refined from petroleum into gasoline, the ones from nonane (C9H20) to hexadecane (C16H34)

into diesel fuel and kerosene (primary component of many types of jet fuel), and the ones from hexadecane upwards into fuel oil and lubricating oil. At the heavier end

of the range, paraffin wax is an alkane with

approximately 25 carbon atoms, while asphalt has 35 and up.

C9H20 to C16H34

asphalt has 35 C and upparaffin waxapproximately 25 carbon atoms

pentane (C5H12) to octane (C8H18)



CH3 CH2

CH

2

CH3

CH3

CH CH3

CH3



NORMAL ALKANE =STRAIGHT CHAIN ISOMER

BRANCHED ALKANES



eclipsed ethane

staggered ethane

CONFORMATIONS

CONFORMATIONAL ISOMERISM is a form of stereoisomerism in which molecules with the same structural formula (same connectivity) exist as different conformational isomers or

conformers in 3-D due to rotations about one or more σ (single) bonds.

The most stable conformer

The most unstable conformer

Natta projection method: Solid or dashed wedged bonds represent bonds pointing above-the-plane or below-the-plane of the paper, respectively.



butane CH3

CH3

H H

HH

CONFORMATIONS

CH3

CH2

CH2

CH3

CH3CH2

CH2

CH3

staggered butane

eclipsed butane

Newman projection formulas

The most unstable conformer

The most stable conformer



IUPAC Rules for Alkane Nomenclature 1. Find and name the longest continuous carbon chain. 2. Identify and name groups attached to this chain. 3. Number the chain consecutively, starting at the end nearest a substituent group.

4. Designate the location of each substituent group by an appropriate number and name. 5. Assemble the name, listing groups in alphabetical order. The prefixes di, tri, tetra etc., used to designate several groups of the same kind, are not considered when alphabetizing.


Name Methyl


ALKYL GROUP is a group differing by one hydrogen from alkane



Group Name

F fluoro

Cl chloro

Br bromo

I iodo

NO2 nitro

NH2 amino

non-alkyl groups:

Systematic nameCommon/Trivial

name(s)Chem.

formula

Chloromethane Methyl chloride CH3Cl

DichloromethaneMethylene chloride

CH2Cl2

Trichloromethane Chloroform CHCl3

TetrachloromethaneCarbon

tetrachloride, Freon 10

CCl4

polytetrafluoroethene PTFE, Teflon -[CF2-CF2]x

methylamine

CH3 NO2

nitromethane

it is the only known surface to which a gecko cannot stick



CH3CH2CH2CH(CH3)2

CH3CH2C(CH3)2CH2CH2CH3

(CH3CH2)2CHCH2CH(CH3)2

PREFIX ROOT ENDING

number and

identity of attached groups

longest carbon chain

functional class

General (IUPAC) nomenclature principle



CH3CH2CH2CH(CH3)2

Functional group is an alkane, therefore suffix = -aneThe longest continuous chain is C5 therefore root = pentThe branch is a C1 alkyl group i.e. a methyl group The first point of difference rule requires numbering from the right as drawn, the substituent locant is 2-

2-methylpentane





CH3CH2CH2CH(CH3)2


2-methylpentane


Functional group is an alkane, therefore suffix = -aneThe longest continuous chain is C6 therefore root = hexThere are two substitutents, both C1 alkyl group i.e. methyl groups The first point of difference rule requires numbering from the left as drawn, the substituent locants are 3- and 3- 3,3-dimethylhexane




CH3CH2CH2CH(CH3)2


2-methylpentane


Functional group is an alkane, therefore suffix = -aneThe longest continuous chain is C6 therefore root = hexThere are two substitutents, both C1 alkyl group i.e. methyl groups The first point of difference rule requires numbering from the left as drawn, the substituent locants are 3- and 3- 3,3-dimethylhexane


4-ethyl-2-methylhexane

Functional group is an alkane, therefore suffix = -aneThe longest continuous chain is C6 therefore root = hexOne C1 alkyl group substituent i.e. a methyl group One C2 alkyl group substituent i.e. an ethyl groupThe first point of difference rule requires numbering from the right as drawn, the substituent locants are 2- and 4-





The longest chain: PENTANE

Substrituents: three methyl groups



The longest chain: PENTANE

Substrituents: three methyl groups

Name: 2,2,4-trimethylpentane



Examples of Simple Cycloalkanes

Name Cyclo-propane

Cyclo-butane

Cyclo-pentane

Cyclo-hexane

Cyclo-heptane

Cyclo-alkane

MolecularFormula

C3H6 C4H8 C5H10 C6H12 C7H14 CnH2n

StructuralFormula

(CH2)n

LineFormula





CYCLOHEXANE



trans-1,2-dichlorocyclohexane cis-1,2-dichlorocyclohexane

Alicyclic compounds can display cis-trans isomerism (geometric isomerism or configuration isomerism)

When the substituents are oriented in opposing directions, the diastereomer is

referred to as trans.

When the substituent groups are oriented in the same direction, the diastereomer is

referred to as cis


1-t-butyl-1-methylcyclohexane

1,1-dimethylcyclohexane

cis-1,2-dimethylcyclohexane

trans-1,2-dimethylcyclohexane




trans-1,2-dibromocyclopentane cis-1,2-dibromocyclopentane

cis-1,2-dimethylcyclopentane trans-1,2-dimethylcyclopentane



Melting (blue) and boiling (pink) points of the first 14 n-alkanes in °C.

R.T.

CH4 to C4H10 alkanes are

gaseous; from C5H12 to C17H36 they

are liquids; and after C18H38 they are

solids

As a rule of thumb, the boiling point rises 20 - 30 °C for each carbon added to the chain

A straight-chain alkane will have a boiling point higher than a branched-chain alkane due to the greater surface area in contact, thus the greater van der Waals (dispersion) forces, between adjacent molecules.



a HOMOLOGOUS SERIES is a series of organic compounds with a similar general

formula, possessing similar chemical properties due to the presence of the same

functional group, and shows a gradation in physical properties as a result of increase in molecular size and mass

HYDROPHOBIC (water in Greek hydro- and fear phobos) refers to the physical property of a molecule (known as a hydrophobe) that is repelled (insoluble in) from a mass of water.

HYDROPHILIC, from the Greek (hydros) "water" and φιλια (philia) "friendship," refers to a physical property of a molecule

that can transiently bond with water (H2O) through hydrogen bonding



CH4 + 2O2 → CO2 + 2H2O + 213 kcal/mol

Provided the combustion is complete, all the hydrocarbons will burn with a blue flame. However, combustion tends to be less complete as the number of

carbon atoms in the molecules rises. That means that the bigger the hydrocarbon, the more likely you are to get a yellow, smoky flame.



Incomplete combustion (where there isn't enough oxygen present) can lead to the formation of carbon or carbon monoxide.

As a simple way of thinking about it, the hydrogen in the hydrocarbon gets the first chance at the oxygen, and the carbon gets whatever is left over!

The presence of glowing carbon particles in a flame turns it yellow, and black carbon is often visible in the smoke. Carbon monoxide is produced as a colourless poisonous gas.

Oxygen is carried around the blood by haemoglobin (US: hemoglobin). Unfortunately carbon monoxide binds to exactly the same site on the

haemoglobin that oxygen does.The difference is that carbon monoxide binds irreversibly - making that particular

molecule of haemoglobin useless for carrying oxygen. If you breath in enough carbon monoxide you will die from a sort of internal suffocation.

2CH4 + 3O2 → 2CO + 4H2O

CH4 + O2 → C + 2H2O



CRACKING is the process whereby complex organic molecules such as kerogens or heavy hydrocarbons are broken down into simpler molecules (e.g. light hydrocarbons) by the breaking of carbon-carbon bonds in the precursors. CRACKING, also referred to as PYROLYSIS, is the breakdown of a large alkane intosmaller, more useful alkanes andan alkene. Simply put, hydrocarbons cracking is the process of breaking long chain hydrocarbons into short ones.

Factory of Shukhov cracking process, Baku, USSR, 1934.



Systematic nameCommon/Trivial

name(s)Chem.

formula

Chloromethane Methyl chloride CH3Cl

DichloromethaneMethylene chloride

CH2Cl2

Trichloromethane Chloroform CHCl3

TetrachloromethaneCarbon

tetrachloride, Freon 10

CCl4

polytetrafluoroethene PTFE, Teflon -[CF2-CF2]x

Alkanes react easily with halogens forming haloalkanes.

CH4 + Cl2 + energy ——> CH3Cl + HCl

CH4 + Cl2 + energy ——> CH3Cl + CH2Cl2 + CHCl3 + CCl4 + HCl

The relative amounts of the various products depend on the proportion of the two reactants used. In the case of methane, a large excess of the hydrocarbon favors formation of methyl chloride as the chief product; whereas, an excess of chlorine favors formation of chloroform and carbon tetrachloride.









Documents

ORGANIC COMPOUNDS : ALKANES Chemistry 21A Dr. Dragan Marinkovic Urea was first discovered in human urine by H.M. Rouelle in 1773 It was synthesized in