Ethanol from ethene and steam. Ethanol can be manufactured by reacting ethene (from cracking cracking: Cracking is the breaking down of large hydrocarbon molecules.
Friday 5 June 2015 – Afternoon GCSE GATEWAY SCIENCE CHEMISTRY B B741/01 Chemistry modules C1, C2, C3 (Foundation Tier) F INSTRUCTIONS TO CANDIDATES. G/KL/Jun16/E4 CH1FP (Jun16CH1FP01) GCSE SCIENCE A CHEMISTRY Foundation Tier Unit Chemistry C1 Thursday Morning Time allowed: 1 hour Materials. A secondary school revision resource for AQA GCSE Chemistry about separating crude oil, alkanes and distillation. Organic chemistry is the chemistry of carbon compounds. All organic compounds contain carbon; however, there are some compounds of carbon that are not.
Alkane - Wikipedia. Chemical structure of methane, the simplest alkane. In organic chemistry, an alkane, or paraffin (a historical name that also has other meanings), is an acyclicsaturatedhydrocarbon. In other words, an alkane consists of hydrogen and carbon atoms arranged in a tree structure in which all the carbon- carbon bonds are single.
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The alkanes range in complexity from the simplest case of methane, CH4 where n = 1 (sometimes called the parent molecule), to arbitrarily large molecules. Besides this standard definition by the International Union of Pure and Applied Chemistry, in some authors' usage the term alkane is applied to any saturated hydrocarbon, including those that are either monocyclic (i. The longest series of linked carbon atoms in a molecule is known as its carbon skeleton or carbon backbone. The number of carbon atoms may be thought of as the size of the alkane. One group of the higher alkanes are waxes, solids at standard ambient temperature and pressure (SATP), for which the number of carbons in the carbon backbone is greater than about 1. With their repeated - CH2- units, the alkanes constitute a homologous series of organic compounds in which the members differ in molecular mass by multiples of 1.
Alkanes are not very reactive and have little biological activity. They can be viewed as molecular trees upon which can be hung the more active/reactive functional groups of biological molecules. The alkanes have two main commercial sources: petroleum (crude oil). They can be: linear (general formula Cn. H2n+2) wherein the carbon atoms are joined in a snake- like structurebranched (general formula Cn. H2n+2, n > 2) wherein the carbon backbone splits off in one or more directionscyclic (general formula Cn. H2n, n > 3) wherein the carbon backbone is linked so as to form a loop.
According to the definition by IUPAC, the former two are alkanes, whereas the third group is called cycloalkanes. Alkanes are the acyclic (loopless) ones, corresponding to k = 0. Isomerism. The simplest isomer of an alkane is the one in which the carbon atoms are arranged in a single chain with no branches. This isomer is sometimes called the n- isomer (n for . However the chain of carbon atoms may also be branched at one or more points. The number of possible isomers increases rapidly with the number of carbon atoms.
For example. For example, 3- methylhexane and its higher homologues are chiral due to their stereogenic center at carbon atom number 3. In addition to the alkane isomers, the chain of carbon atoms may form one or more loops. Such compounds are called cycloalkanes. Nomenclature. Unbranched, saturated hydrocarbon chains are named systematically with a Greek numerical prefix denoting the number of carbons and the suffix .
This is because shorter chains attached to longer chains are prefixes and the convention includes brackets. Numbers in the name, referring to which carbon a group is attached to, should be as low as possible so that 1- is implied and usually omitted from names of organic compounds with only one side- group. Symmetric compounds will have two ways of arriving at the same name. Linear alkanes. Although this is not strictly necessary, the usage is still common in cases where there is an important difference in properties between the straight- chain and branched- chain isomers, e. Alternative names for this group are: linear paraffins or n- paraffins. The members of the series (in terms of number of carbon atoms) are named as follows: methane, CH4 – one carbon and four hydrogenethane, C2. H6 – two carbon and six hydrogenpropane, C3.
H8 – three carbon and 8 hydrogenbutane, C4. H1. 0 – four carbon and 1. C5. H1. 2 – five carbon and 1.
C6. H1. 4 – six carbon and 1. The first four names were derived from methanol, ether, propionic acid and butyric acid, respectively (hexadecane is also sometimes referred to as cetane).
Alkanes with five or more carbon atoms are named by adding the suffix- ane to the appropriate numerical multiplier prefix. Hence, pentane, C5. H1. 2; hexane, C6. H1. 4; heptane, C7. H1. 6; octane, C8.
H1. 8; etc. The prefix is generally Greek, however alkanes with a carbon atom count ending in nine, for example nonane, use the Latin prefix non- . For a more complete list, see List of alkanes. Branched alkanes. Cycloalkanes are named as per their acyclic counterparts with respect to the number of carbon atoms in their backbones, e. C5. H1. 0) is a cycloalkane with 5 carbon atoms just like pentane (C5.
H1. 2), but they are joined up in a five- membered ring. In a similar manner, propane and cyclopropane, butane and cyclobutane, etc. Substituted cycloalkanes are named similarly to substituted alkanes — the cycloalkane ring is stated, and the substituents are according to their position on the ring, with the numbering decided by the Cahn–Ingold–Prelog priority rules. Together, alkanes are known as the paraffin series.
Trivial names for compounds are usually historical artifacts. They were coined before the development of systematic names, and have been retained due to familiar usage in industry. Cycloalkanes are also called naphthenes. It is almost certain that the term paraffin stems from the petrochemical industry.
Branched- chain alkanes are called isoparaffins. The use of the term .
Stronger intermolecular van der Waals forces give rise to greater boiling points of alkanes. As the boiling point of alkanes is primarily determined by weight, it should not be a surprise that the boiling point has almost a linear relationship with the size (molecular weight) of the molecule. As a rule of thumb, the boiling point rises 2.
For example, compare isobutane (2- methylpropane) and n- butane (butane), which boil at . That is, (all other things being equal) the larger the molecule the higher the melting point. There is one significant difference between boiling points and melting points. Solids have more rigid and fixed structure than liquids. This rigid structure requires energy to break down. Thus the better put together solid structures will require more energy to break apart.
For alkanes, this can be seen from the graph above (i. The odd- numbered alkanes have a lower trend in melting points than even numbered alkanes. This is because even numbered alkanes pack well in the solid phase, forming a well- organized structure, which requires more energy to break apart. The odd- numbered alkanes pack less well and so the . For this reason, they do not form hydrogen bonds and are insoluble in polar solvents such as water.
Since the hydrogen bonds between individual water molecules are aligned away from an alkane molecule, the coexistence of an alkane and water leads to an increase in molecular order (a reduction in entropy). As there is no significant bonding between water molecules and alkane molecules, the second law of thermodynamics suggests that this reduction in entropy should be minimized by minimizing the contact between alkane and water: Alkanes are said to be hydrophobic in that they repel water. Their solubility in nonpolar solvents is relatively good, a property that is called lipophilicity. Different alkanes are, for example, miscible in all proportions among themselves. The density of the alkanes usually increases with the number of carbon atoms but remains less than that of water. Hence, alkanes form the upper layer in an alkane–water mixture. Molecular geometry.
It is derived from the electron configuration of carbon, which has four valence electrons. The carbon atoms in alkanes are always sp. These orbitals, which have identical energies, are arranged spatially in the form of a tetrahedron, the angle of cos. The former result from the overlap of an sp. The bond lengths amount to 1. Structural formulae that represent the bonds as being at right angles to one another, while both common and useful, do not correspond with the reality.
Conformation. There is a further degree of freedom for each carbon–carbon bond: the torsion angle between the atoms or groups bound to the atoms at each end of the bond. The spatial arrangement described by the torsion angles of the molecule is known as its conformation. If one looks down the axis of the C–C bond, one will see the so- called Newman projection. The hydrogen atoms on both the front and rear carbon atoms have an angle of 1. However, the torsion angle between a given hydrogen atom attached to the front carbon and a given hydrogen atom attached to the rear carbon can vary freely between 0. This is a consequence of the free rotation about a carbon–carbon single bond.
Despite this apparent freedom, only two limiting conformations are important: eclipsed conformation and staggered conformation. The two conformations, also known as rotamers, differ in energy: The staggered conformation is 1. J/mol lower in energy (more stable) than the eclipsed conformation (the least stable). This difference in energy between the two conformations, known as the torsion energy, is low compared to the thermal energy of an ethane molecule at ambient temperature. There is constant rotation about the C–C bond. The time taken for an ethane molecule to pass from one staggered conformation to the next, equivalent to the rotation of one CH3 group by 1.
For this reason, alkanes are usually shown in a zigzag arrangement in diagrams or in models. The actual structure will always differ somewhat from these idealized forms, as the differences in energy between the conformations are small compared to the thermal energy of the molecules: Alkane molecules have no fixed structural form, whatever the models may suggest.
Spectroscopic properties. Alkanes are notable for having no other groups, and therefore for the absence of other characteristic spectroscopic features of a different functional group like –OH, –CHO, –COOH etc. Infrared spectroscopy. The carbon–hydrogen bending modes depend on the nature of the group: methyl groups show bands at 1. Carbon chains with more than four carbon atoms show a weak absorption at around 7.