Alkane:Member of a group of hydrocarbons having the general formula
CnH2n + 2, commonly known as
paraffins.
As they contain only
single covalent bonds, alkanes are said to be
saturated.
Lighter alkanes, such as methane, ethane, propane, and butane, are colourless gases;
heavier ones are liquids or solids. In nature they are found in natural gas and petroleum.
Their principal reactions are combustion and bromination.
CH4 + 2O2 → CO2 + 2H2O
C3H8 + 5O2 → 3CO2 + 4H2O
C2H6 + Br2 →200°C C2H5Br + HBr
Alkane doesn't change the colour of bromine water
Alkane don’t solouble in heavy H2so4 and sodium hidroxice solution
alkane haven’t positive test to unio transmite by iodine .Physical
phsical properties for identify alkane:1.melting point
2.boiling point
3.density
4.refraction index
IR Spectroscopy Tutorial for identify Alkanes:
The spectra of simple alkanes are characterized by absorptions due to C–H stretching and bending (the C–C stretching and bending bands are either too weak or of too low a frequency to be detected in IR spectroscopy). In simple alkanes, which have very few bands, each band in the spectrum can be assigned.
•
C–H stretch from 3000–2850 cm-1
• C–H bend or scissoring from 1470-1450 cm-1
• C–H rock, methyl from 1370-1350 cm-1
• C–H rock, methyl, seen only in long chain alkanes, from 725-720 cm-1 The IR spectrum of octane is shown below. Note the strong bands in the 3000-2850 cm-1 region due to C-H stretch. The C-H scissoring (1470), methyl rock (1383), and long-chain methyl rock (728) are noted on this spectrum. Since most organic compounds have these features, these C-H vibrations are usually not noted when interpreting a routine IR spectrum.
The region from about 1300-900 cm-1 is called the fingerprint region. The bands in this region originate in interacting vibrational modes resulting in a complex absorption pattern. Usually, this region is quite complex and often difficult to interpret; however, each organic compound has its own unique absorption pattern (or fingerprint) in this region and thus an IR spectrum be used to identify a compound by matching it with a sample of a known compound.
Researchers in LBL's Chemical Sciences Division (CSD): took an important step towards harnessing the vast potential of one of nature's most plentiful materials when they determined how metals can chemically interact with the large class of naturally occurring hydrocarbons known as alkanes.
Alkanes are compounds of carbon and hydrogen atoms held together by single bonds. The simplest and most abundant is methane, the primary constituent of natural gas. Chemists have long coveted the
use of alkanes as feedstock for clean-burning fuels and a host of petrochemicals, including plastics, solvents, synthetic fibers, and pharmaceutical drugs. The problem has been that the bonds between an alkane's hydrogen and carbon atoms are so strong as to render alkanes generally unreactive. LBL chemists have shown that it is possible to
insert the metal centers of certain metal complexes into the carbon-hydrogen (C-H) bonds of alkanes to form weaker carbon-metal bonds that are much more chemically useful. This illustration shows the energy barrier associated with the insertion of an iridium metal center (the blue iridium atom) into the C-H bond (red carbons and white hydrogens) of an "alkane complex." (The C-H insertion proceeds from left to right.) In the transition state of the reaction, one can see the C-H bond stretching as the iridium-
carbon and iridium-hydrogen bonds start to form.
CSD researchers, led by chemist and UC Berkeley professor Robert Bergman, winner of an E.O. Lawrence Award in 1993 for his alkane studies, have been
working with organometallic complexes that can break carbon-hydrogen (C-H) bonds in alkanes and insert a metal atom (the metals that they have used so far are iridium, rhodium and rhenium). This leads to the formation of carbon-metal-hydrogen complexes that are much more chemically reactive than alkanes and better able to be converted into products. Utilizing liquefied krypton and xenon as solvents so that the C-H activation process could be carried out at low temperatures (to slow the process down), Bergman and his group discovered that metal noble gas and metal alkane "solvate" complexes were formed as intermediates in the activating reaction. These weakly bound "alkane complexes" are formed before the C-H bonds are broken.
By combining the data obtained in their liquefied noble gas experiments, with gas phase data obtained in experiments conducted by LBL-UCB chemist Brad Moore and his group of researchers, Bergman and his group have been able to put together a unified picture of the C-H activation process.
This picture shows that
larger alkane molecules, such as cyclohexane, bind more strongly to the metal center in the solvate than smaller alkanes, such as ethane. This size-binding effect may in part explain why it is so difficult to activate methane, the smallest but most important alkane. Understanding the factors behind this difficulty could provide a solution for activating methane and converting it into useful products.
This past year, Bergman and his group were also able to measure the energy barrier that must be crossed in order for the C-H bond-breaking reaction to occur in the alkane complex.
The energy barrier was found to be approximately 5 kilocalories per mole.
