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10. Organic Chemistry http://chemmaster.co.in/showchapter.php?id=20&id2=161&title=Hydrocarbons Boiling Points: http://www.colby.edu/chemistry/cmp/cmp.html http://masterorganicchemistry.com/2010/10/25/3-trends-that-affect-boiling-points/
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Origins Originally defined as the chemistry of living materials or originating from living sources. Wohler synthesized urea from non organic sources (1800 – 1882) Now generally defined as the chemistry of carbon and its compounds.
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Why is carbon so special?
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Carbon can form single, double and triple bonds with itself http://wps.prenhall.com/wps/media/objects/3311/3391006/blb0809.html The bond length is defined as the distance between the nuclei of the atoms involved in the bond.
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Bond enthalpy is the enthalpy change, H, for the breaking of a particular bond in a mole of gaseous substance.
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Carbon can catenate This property of linking of atoms of one element with one another forming chains of identical atoms is called catenation.
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Hydrocarbons are organic compounds that contain mainly hydrogen and carbon Types : Alkanes Alkenes Alkynes Aromatic Hydrocarbons 7
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http://www.ivy-rose.co.uk/Chemistry/Organic/Homologous-Series.php A Homologous Series is one in which all the members have the same general formula. The neighbouring members of the series differ by CH 2 and they show similar chemical properties and a gradual change in their physical properties.
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A series of prefixes are used to designate the number of carbon atoms in a carbon chain: Naming Hydrocarbons meth1 Chex6 C eth2 Chept7 C prop3 Coct8 C but4 Cnon9 C pent5 Cdec10 C 9
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Alkanes have only carbon to carbon single bonds. General Formula C n H 2n+2 Alkane Structures 10
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Homologous Series: A homologous series of alkanes CH 4 Methane C2H6C2H6 Ethane C3H8C3H8 Propane C 4 H 10 Butane C 5 H 12 Pentane Each compound in this series differs from the previous compound by a –CH 2 –
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Methane CH4 Ethane C2H6 CH3CH3 Propane C3H8 CH3CH2CH3 Butane C4H10 CH3CH2CH2CH3 Pentane C5H12 CH3CH2CH2CH2CH3
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Isomers Structural Isomers are compounds with the same chemical formula but a different structural formula. As the number of carbon atoms in an alkane molecule increases, so do the possibilities for isomerism of this kind. There are three isomeric pentanes, all with the C 5 H 12, five isomeric hexanes, C 6 H 14 14
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General Properties of Alkanes The boiling points of alkanes are very low for their molecular mass. This is because the molecule is completely nonpolar( inertness) It increases with an increase in mass.
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Structural Isomers
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Boiling Points of Alkanes http://wiki.chemeddl.org/index.php/8.2_Organic_Compounds:_Hydrocarbons The more spherical the isomer, the lower boiling point( less dispersion forces) due to less surface area to form intermolecular bonds.
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Alkenes have one carbon to carbon double bond C=C Since there are fewer hydrogen atoms in alkenes as a result of the double bond, alkenes are referred to as unsaturated. Alkanes on the other hand have the maximum number of hydrogen atoms. They are referred to as saturated. Alkenes 19
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Like alkanes, alkenes can have branched or consecutive chains. In the larger alkenes there are also multiple locations for the C=C. Hence multiple structural isomers are possible. Alkene Structures Branched chain Straight chain. 20
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Alkynes have one (or more) carbon to carbon triple bonds Since there are fewer hydrogen atoms in alkynes as a result of the triple bond, alkynes like alkenes are referred to as unsaturated. Alkynes 21
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Like alkanes and alkenes, alkynes can have branched or consecutive chains. In the larger alkenes there are also multiple locations for the C=C. Multiple structural isomers are possible. The branch cannot originate on one of the carbons making up the triple bond Alkyne Structures Branched chain. The triple bond can occur in one of the branches but branches cannot be attached to any carbon in the triple bond Straight chain. The triple bond is between the first and second carbon Straight chain. The triple bond is between the second and third carbon 22
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Functional Groups In organic chemistry, functional groups are specific groups of atoms within molecules, that are responsible for the characteristic chemical reactions of those 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. http://www.3rd1000.com/chem301/chem301a.htm
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Benzene
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I-Alkanes Alkanes are very unreactive due to single C C bonds. All combustion reactions are highly exothermic.(low polarity &van der waals) I.Complete Combustion: 2C 8 H 18 + 25O 2 => 16CO 2 + 18 H 2 O II. Incomplete Combustion C 8 H 18 + 9O 2 => 2CO 2 + 9 H 2 O + C + 5CO C and CO are emitted as particulates. Page 193 CC
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Combustion of Hydrocarbons This is effectively a technical word for burning. Complete combustion produces CO 2 and H 2 O, incomplete combustion produces CO, C and H 2 O,where there is C 3 H 8 + 5O 2 => 3CO 2 + 4H 2 O
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Resonance –Polarity of Carboxylic acids
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Hydrocarbons that exist in chains are known as aliphatic hydrocarbons The ends of a chain may be joined to form a ring structure. These compounds are known as cyclic structures Ring Structures 30
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The benzene ring is a common structure in organic molecules It consists of 6 carbon atoms and 6 hydrogen atoms. One would predict that there should also be 3 C=C bonds in a benzene ring Aromatic Structures 31
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Further investigation reveals that the double bonds are not distinct in benzene. Rather it is a resonance hybrid. Either of these structures could be used to represent benzene. Aromatic Structures 32
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Research shows that there are no differences in the C to C bonds in benzene. The current view of benzene holds that there are 6 C-C single bonds and 3 pairs or 6 delocalized electrons Aromatic Structures 33
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The structure of benzene is shown as either of these two structures, or as a circle in a hexagon which depicts that the electrons are delocalized Aromatic Structures 34
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Halogenoalkanes or Alkyl Halides Halogenoalkanes are compounds in which one or more hydrogen atoms in an alkane have been replaced by halogen atoms (fluorine, chlorine, bromine or iodine). Halogenoalkanes are commonly known as alkyl halides 35
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Halogenoalkanes or Alkyl Halides Depending on the location of the halogen atom, halogenoalkanes may be primary secondary or tertiary 36
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Boiling Points of Halogenoalkanes The boiling point depends on the halide Cl < Br < I The boiling points increase as the chain length increases 37
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Solubility of Halogenoalkanes The halogenoalkanes are only very slightly soluble in water. The attractions between the halogenoalkane molecules (van der Waals dispersion and dipole-dipole interactions) are relatively strong Halogenoalkanes are only slightly polar and do not effectively break the hydrogen bonds between water molecules. Halogenoalkanes are soluble in non polar or less polar organic solvents such as alcohol, ether, and benzene. 38
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Functional Groups http://www.ivy-rose.co.uk/Chemistry/Organic/Homologous- Series.phphttp://www.ivy-rose.co.uk/Chemistry/Organic/Homologous- Series.php
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Alcohols http://www.physchem.co.za/OB12- mat/organic2.htm#alkanolshttp://www.physchem.co.za/OB12- mat/organic2.htm#alkanols
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Carboxylic Acids http://www.physchem.co.za/OB12- mat/organic2.htm#acidshttp://www.physchem.co.za/OB12- mat/organic2.htm#acids
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Carboxylic acids have a higher boiling boint than the alkanols with the same number of carbon atoms. This is not solely due to an increase in molar mass (14 units), but rather because carboxylic acids tend to be more strongly hydrogen bonded than alkanols, and even have a tendency to form dimers.
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Aldehydes and Ketones http://www.physchem.co.za/OB12- mat/organic2.htm#ketoneshttp://www.physchem.co.za/OB12- mat/organic2.htm#ketones
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Amines and Amides http://www.physchem.co.za/OB12- mat/organic2.htm#amineshttp://www.physchem.co.za/OB12- mat/organic2.htm#amines
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Esters http://www.physchem.co.za/OB12- mat/organic2.htm#acidshttp://www.physchem.co.za/OB12- mat/organic2.htm#acids
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Halogenoalkanes Have the general formula R-X where R is an alkyl group and X is a halogen CCCl H H H H H Chloroethane
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Functional group Isomerism http://www.creative-chemistry.org.uk/molecules/isomers.htm Functional isomerism, an example of structural isomerism, occurs substances have the same molecular formula but different functional groups. This means that functional isomers belong to different homologous series.
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Volatility Is a measure of how easily a substance evaporates. A high volatile substance evaporates easily and has a low boiling point. Volatile organic compounds (VOCs) are organic chemicals that have a high vapor pressure at ordinary, room- temperature conditions. Their high vapor pressure results from a low boiling point, which causes large numbers of molecules to evaporate from the liquid or solid form of the compound and enter the surrounding air. An example is formaldehyde, with a boiling point of –19 °C (–2 °F), slowly exiting paint and getting into the air.organic chemicalsvapor pressureroom- temperatureevaporate formaldehydepaint
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Note the strong influence of hydrogen bonding which explains the low volatility (high boiling point) of HF, H 2 O and NH 3. Also note that volatility generally decreases (B.Pt. increases) down a group (e.g. CH 4, SiH 4, GeH 4 etc) as the polarisability of the molecules increases and their temporary dipoles get larger leading to greater temporary dipole/temporary dipoles interactions (van der Waals' forces).
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Vapor pressure is the pressure caused by a liquid's own vapor. 52 VAPOUR PRESSURE http://www.pkwy.k12.mo.us/west/teachers/anderson/pack5/boil/boil.html
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