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Experiment #3 - Hydrocarbons

CCCCCCCCHHHHHHHHHHHHHHHHHHCCCCCCCCHHHHHH HHHCHHHCHHHHHHHHHCHHHCCCCCCCHHCHHHHHHHHH HHHHH octane - unbranched (straight-chain)4-ethyl-2-methyloctane - branchedethylcyclohexane - cyclicFigure 1 - Unbranched, branched, andcyclic #3 - HydrocarbonsIntroductionOrganic chemistry is the chemistry of thecompounds of carbon. Currently over twentymillion compounds have been reported in thechemical literature; about 90% of them areorganic, ie they contain carbon. The remainingcompounds are called inorganic and are formedfrom the other elements, of which there areabout 100.

Organic chemistry is the chemistry of the compounds of carbon. Currently over twenty ... They are soluble in solvents of low polarity. They are not soluble in water, which is very polar, because the water molecules attract each other ... Experiment #3 Hydrocarbons Page 4 C 3H 8 + 5 O 2 3 CO 2 + 4 H 2O H 3CCH CHCH 3 H 3CCH CHCH 3 Br Br + H 3CC ...

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Transcription of Experiment #3 - Hydrocarbons

1 CCCCCCCCHHHHHHHHHHHHHHHHHHCCCCCCCCHHHHHH HHHCHHHCHHHHHHHHHCHHHCCCCCCCHHCHHHHHHHHH HHHHH octane - unbranched (straight-chain)4-ethyl-2-methyloctane - branchedethylcyclohexane - cyclicFigure 1 - Unbranched, branched, andcyclic #3 - HydrocarbonsIntroductionOrganic chemistry is the chemistry of thecompounds of carbon. Currently over twentymillion compounds have been reported in thechemical literature; about 90% of them areorganic, ie they contain carbon. The remainingcompounds are called inorganic and are formedfrom the other elements, of which there areabout 100.

2 That carbon so dominatescompound formation is a result of the fact that itis almost unique in its ability to form longchains with other carbon atoms. [Carbon sneighbor in the periodic table, silicon, can dothis but rarely does.] These chains with onecarbon joined to a second and the secondjoined to a third, etc., can be branched, ie,chains of carbon atoms can be attached tocarbons in the original chain. It is also possiblefor one carbon in a chain to become bonded toanother carbon in that chain, resulting in aclosed ring of atoms. We call these there are so many organiccompounds it is fortunate that we can organizethem into various groups that have somesimilarity to each other.

3 For example, one largegroup of organic compounds is known as thehydrocarbons because members of this groupcontain only carbon and hydrogen and no otherelements. Figure 1 shows examples of branched, unbranched and cyclic is possible to subdivide the hydrocarbon group of compounds based on thebonding between the carbons. If all the carbon-carbon bonds are single, the compoundis an alkane. If at least one of the carbon-carbon bonds in the compound is a doublebond, and the remaining carbon-carbon bonds are single, the compound is an alkene. Ifat least one of the carbon-carbon bonds in the compound is a triple bond, and theremaining carbon-carbon bonds are single, the compound is an alkyne.

4 If the compoundcontains a six carbon ring that has alternating double and single bonds around the ring(three double and three single), we say that ring, and the compound, is aromatic. Anaromatic ring looks like an alkene with three double bonds because that s the way wedraw it using Lewis structures. However, the actual bonding in such a ring isconsiderably different from that in alkenes and, consequently, many of the chemicalproperties are different also. Therefore, we place these compounds in a separate family. By the way, the term aromatic as used here has nothing to do with #3 HydrocarbonsPage 2 Hydrocarbons may be saturated or unsaturated.

5 A saturated hydrocarbon is onethat is maxed out in terms of the number of hydrogens that can be present given thenumber of carbons in the compound; it is impossible to add more hydrogen atoms to thecompound so it is saturated with hydrogen. Acyclic (no rings) alkanes are saturated;there is no way additional hydrogens can be added while keeping the same number ofcarbons and maintaining normal bonding between the atoms. Alkenes, alkynes, aromaticcompounds, and cyclic alkanes are unsaturated because hydrogen can be added to them,in theory and usually in practice, making them into acyclic alkanes.

6 Some PropertiesSome molecules carry an electrical charge because there is a difference betweenthe number of electrons (each with a -1 charge) and the number of protons (each with a+1 charge) in the molecule. We call molecules of this type ions. The ammonium ion,NH4+, has a +1 charge because it has 11 protons (7 from nitrogen and 4 from thehydrogens) and 10 electrons (2 in nitrogen s first shell, and 8 in its second shell [whichare used to bond the hydrogens to the nitrogen]). So, with 11 plus charges and 10 minuscharges, the ammonium ion has a net charge of +1.

7 Most molecules are not ions (and wesimply call them molecules); in other words they are electrically neutral they have acharge of 0 because they have the same number of protons as CHCH3H2H3 CCH CHCH3HH+catalystH3CC CCH3catalyst+H3CC CCH3 HHHHH22 CCCCCCHHHHHH catalystH23 CCCCCCHHHHHHHHHHHH+H2in theory,if not easilydone inpracticeCCCCCCHHHHHHHHHHHHHH unsaturatedcompoundssaturatedcompoundsEx periment #3 HydrocarbonsPage 3 vvvmmmn = ss=sinsinvacuummateriallight beamlight beamFigure 2 - Index of RefractionIn some molecules, even though the net charge is 0, the distribution of positivecharges (protons)

8 And negative charges (electrons) within the molecule is not the same. Such a molecule has a lopsided charge distribution one side of the molecule is electronrich (has a partial negative charge) and the other side is proton rich (has a partial positivecharge). We say that such a molecule is polar or that it has a dipole moment. The morelopsided the charge distribution, the larger the dipole moment and the more polar themolecule. In some molecules the distribution of positive and negative charges is thesame; these molecules have no dipole moment and are nonpolar.

9 When organicmolecules are polar it is usually because there are one or more highly electronegativeatoms on one side of the molecule. Electronegative atoms are those that attract electronstoward themselves; common examples are nitrogen, oxygen, and the halogens, especiallyfluorine and molecules attract each other because the negative side of one attracts thepostive side of another (opposite charges attract). The more polar the molecules themore they attract each other. It is also true that nonpolar molecules do not attract eachother as strongly as polar molecules do and polar molecules are not attracted to nonpolarmolecules as much as polar molecules are attracted to each are molecules that have little or no polarity because they do notcontain electronegative atoms.

10 They are soluble in solvents of low polarity. They are notsoluble in water, which is very polar, because the water molecules attract each otherstrongly (and are not nearly as interested in attracting nonpolar molecules). Density is the mass of a material divided by its volume; it is often expressed interms of grams of mass per cubic centimeter of volume. The density of water, forexample, is gram per cubic centimeter. For the most part, Hydrocarbons are lessdense than water, so, given their insolubility in water, they float on it. Crude oil and itsderivatives gasoline, kerosine, and fuel oil are mainly Hydrocarbons ; none of these issoluble in water and they float on its surface since they are less dense than index of refraction, n, of a compound isthe speed of light in a vacuum, sv divided by thespeed of light in that substance, sm.


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