In petrochemistry, petroleum geology and organic chemistry, cracking is the process whereby complex organic molecules such as kerogens or long-chain hydrocarbons are broken down into simpler molecules such as light hydrocarbons, by the breaking of carbon-carbon bonds in the precursors. The rate of cracking and the end products are strongly dependent on the temperature and presence of catalysts. Cracking is the breakdown of a large alkane into smaller, more useful alkenes. Simply put, hydrocarbon cracking is the process of breaking a long chain of hydrocarbons into short ones. This process requires high temperatures.[1]
More loosely, outside the field of petroleum chemistry, the term "cracking" is used to describe any type of splitting of molecules under the influence of heat, catalysts and solvents, such as in processes of destructive distillation or pyrolysis.
what does cracking mean in organic chemistry
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But cracking doesn't have to be a bad thing. Sure, smashing a plate isn't much fun, but unless you break open an egg, you'll never be able to make an omelette with the tasty white and yolk inside. Cracking an object into smaller pieces to make it more useful is much like chemical cracking.
When we crack a Christmas cracker, we snap it in half to reveal a silly joke and paper hat. When we crack a coconut, we are rewarded with a feast of refreshingly cool coconut water. In both cases, we break a larger object apart into smaller pieces to make it more useful. This also happens in cracking in chemistry.
The process is random, meaning that we can't control exactly which molecules we end up with. However, it doesn't matter so much - both types of products are much more useful to us than the original longer-chain hydrocarbons. With cracking, we can turn relatively useless molecules that we probably wouldn't otherwise use into relatively useful molecules that massively enhance our lives.
Thermal cracking involves putting the hydrocarbon alkanes under extreme heat and pressure for a brief period of time, usually only one second. We typically use a very high temperature of 700-1200 K and a high pressure of 7000 kPa. The alkane splits homolytically, meaning one electron from the bonded pair goes to each of the new molecules formed. This forms two free radicals.
Cracking is a largely random process. It is impossible to predict exactly which molecules will be produced. This means there are multiple different equations and potential products for each reaction, and your examiner could test you in various ways. This will typically involve finding an unknown hydrocarbon reactant or product. However, it's easy enough to 'crack' cracking equations! The important thing to remember is that the equation has to be balanced: the numbers of carbon atoms and hydrogen atoms on each side of the equation must be the same.
The concept of cracking in organic chemistry is related to the action of breaking down large chains of carbon into smaller chains obtaining light hydrocarbons. This process is widely used in the petrochemical industry.
Thermal cracking doesn't go via ionic intermediates like catalytic cracking. Instead, carbon-carbon bonds are broken so that each carbon atom ends up with a single electron. In other words, free radicals are formed.
The demand for petrol is greater than the gasoline fraction obtained by distilling crude oil. Cracking larger hydrocarbons produces smaller alkanes that can be converted into petrol. It also produces small alkenes, which are used make many other useful organic chemicals (petrochemicals), especially plastics. This experiment models the industrial cracking process.
In the chlorination of methane, we see a particular property of hydrogen atoms in organic molecules in general. They are labile, meaning they can be easily exchanged for other things. In this case, the bonding pair of the C-H bond moves to one Chlorine atom in the Cl2 while the Cl-Cl bonding pair jumps to form a new bond between the other Cl and the Carbon atom.
The cracking reaction involves the homolitic cleavage of a C-C bond. This reaction needs a catalyst to function with any efficiency. This means that the two electrons are divided evenly between the two atoms. This results in two fragments, each with a lone electron (dangling bond). The two fragments are radicals and are not very stable. To stabilize the pair, a hydrogen homolitically cleaves from a carbon neighboring one of the two carbons used to be bonded together leaves that carbon and migrates over to the other fragment to complete the bonding on that fragment. The two carbons on the fragment from which the hydrogen left now form a double C=C bond and all electrons are paired up again. See the diagram below for a visual representation.
Soil is a combination of air, water, minerals, and organic matter that forms at the transition between biosphere and geosphere. Soil is made when weathering breaks down bedrock and turns it into sediment. If erosion does not remove the sediment significantly, organisms can access the mineral content of the sediments. These organisms turn minerals, water, and atmospheric gases into organic substances that contribute to the soil.
The nature of the soil, meaning its characteristics, is determined primarily by five components: 1) the mineralogy of the parent material; 2) topography, 3) weathering, 4) climate, and 5) the organisms that inhabit the soil. For example, soil tends to erode more rapidly on steep slopes so soil layers in these areas may be thinner than in flood plains, where it tends to accumulate. The quantity and chemistry of organic matter of soil affects how much and what varieties of life it can sustain. Temperature and precipitation, two major weathering agents, are dependent on climate. Fungi and bacteria contribute organic matter and the ability of soil to sustain life, interacting with plant roots to exchange nitrogen and other nutrients.
Cracking is the process of taking bigger organic molecules, like the hydrocarbons from crude oil, and turning them into smaller ones. So, broadly speaking, cracking reactions are decomposition reactions.
Ethylene is a critical building block for the petrochemical industry, and is among the most produced organic compounds. It is usually produced in steam-cracking units from a range of petroleum-based feedstocks, such as naphtha, and is used in the manufacture of several major derivatives. 2ff7e9595c
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