Organic Oxidation-Reduction Reactions
In General Chemistry, Oxidation-reduction reactions was something you memorized. Without mentioning electrochemistry, (oops just mentioned it), the loss or gain of electrons was “OIL RIG” or “LEO GER”. That is not quite how it is in Organic chemistry. It’s a bit different. In organic oxidation-reduction reactions, loss of electrons is oxidation and gain of electrons is reduction but with respect to carbon (the central character) itself.
Organic Oxidation-Reduction Reactions in Chemistry
Methane for example is reduced. It’s surrounded by electrons because the only thing attached to it is hydrogen. Hydrogen (2.1) has about the same electronegativity as carbon (2.5). We are concerned with covalent bonds. This is a nonpolar bond.
When carbon is attached to oxygen on the other hand, the amount of electron density (not a whole electron) is decreased or lost. This is oxidation. The most oxidized forms of carbon have their electrons far from the nucleus surrounding an atom more electronegative than it. The carbon in CCl4 or carbon tetrachloride is highly oxidized because its 4 electrons are closer to chlorine than itself. Therefore it and carbon dioxide, carbon monoxide and so on, with many polar covalent bonds are highly oxidized.
When carbon is surrounded by hydrogen, the amount of electron density around carbon is highest (Silicon adds more than hydrogen but that’s another story). Reduction therefore, is any reaction where carbon gains hydrogen. The gain in hydrogen is and must be an exchange for a similarly electronegative atom (read: hydrogen) than carbon and is called a reduction reaction.
If we take a single carbon through the limits of reduction and oxidation, it would look like the following:
Since carbon keeps more of its electron density to the left, it is more reduced. Conversely, it loses much to oxygen on the right side so it is oxidized. It does not have to be oxygen for a chemical change to be an oxidation. Any element that replaces hydrogen and is more electronegative than carbon is an oxidation. Any reaction that removes an bond to a more electronegative atom in exchange for hydrogen is a reduction.
Catalytic Hydrogenation: Which is it?
Since each carbon gains a hydrogen atom and the hydrogen comes from one face of a palladium (metal) surface, they will almost always come from the same direction (on paper that is) and each carbon also gains a bond to a less electronegative atom (sp3 carbon from an sp2 carbon). This is a reduction.
It’s also a favorite reaction because it is easily memorized. Make no mistake however, this is a flash card reaction. The others are not this simple. The point is that there’s no mechanism to draw (no arrows to push) so people who are new love it. This reaction can be learned by a junior high school student, literally.
Halogenation: Which is it?
or abbreviated this way:
Each carbon of the former double bond (alkene) gained an electronegative element. Both carbons are oxidized. This is an oxidation reaction. But not one you can flashcard. If you’ve been shown the mechanism (lavender arrows above) you have to work the problem the same way. No flash cards until you’ve written it out from memory at least a few times.
Organic Oxidation-Reduction Reactions Katika kemia ya jumla, Oxidation-reduction reactions ilikuwa kitu ulichokumbuka. Bila kutaja electrochemistry, (oops tu zilizotajwa), hasara au faida ya elektroni ilikuwa <unk>OIL RIG<unk> au <unk>LEO GER<unk>. Hiyo si kabisa jinsi ni katika kemia ya kikaboni. Ni tofauti kidogo. Katika athari za kikaboni za oxidation-reduction, hasara ya elektroni ni oxidation na faida ya elektroni ni kupunguzwa lakini kwa heshima ya kaboni (sifa ya kati) yenyewe. Organic Oxidation-Reduction Reactions in Chemistry Methane kwa mfano hupunguzwa. Ni kuzungukwa na elektroni kwa sababu kitu pekee kushikamana na ni hidrojeni. Hidrojeni (2.1) ina kuhusu electronegativity sawa na kaboni (2.5). Sisi ni wasiwasi na vifungo covalent. Hii ni dhamana isiyo ya mviringo. Wakati kaboni imeunganishwa na oksijeni kwa upande mwingine, kiasi cha wiani wa elektroni (si elektroni nzima) hupungua au kupotea. Hii ni oxidation. Aina nyingi za kaboni zilizo na oksidi zina elektroni zao mbali na kiini kinachozunguka atomu yenye nguvu zaidi ya elektronegatifiki kuliko hiyo. Carbon tetrachloride (CCT) ni kemikali ya carbon tetrachloride ambayo ina elektroni nne ambazo ni karibu zaidi na klorini. Kwa hiyo, pamoja na kaboni dioksidi, kaboni monoksidi na kadhalika, na vifungo vingi vya polar covalent ni sana oxidized. Wakati kaboni ni kuzungukwa na hidrojeni, kiasi cha wiani wa elektroni karibu kaboni ni ya juu (Silicon anaongeza zaidi ya hidrojeni lakini hiyo ni hadithi nyingine). Kupunguza kwa hiyo, ni athari yoyote ambapo kaboni hupata hidrojeni. Kuongezeka kwa hidrojeni ni na lazima kuwa kubadilishana kwa atomu sawa ya electronegative (soma: hidrojeni) kuliko kaboni na inaitwa athari ya kupunguzwa. Ikiwa tunachukua kaboni moja kupitia mipaka ya kupunguzwa na oxidation, itaonekana kama ifuatavyo: Kwa kuwa kaboni inahifadhi zaidi ya wiani wake wa elektroni upande wa kushoto, ni zaidi ya kupunguzwa. Kinyume chake, inapoteza oksijeni nyingi upande wa kulia kwa hivyo hutiwa oksidi. Si lazima iwe oksijeni kwa ajili ya mabadiliko ya kemikali kuwa oxidation. Kiungo chochote kinachobadilisha hidrojeni na kuwa na electronegative zaidi kuliko kaboni ni oxidation. Mmenyuko wowote unaoa uhusiano na atomu yenye electronegative zaidi kwa kubadilishana na hidrojeni ni kupunguzwa. Catalytic Hydrogenation: Ni ipi? Kwa kuwa kila kaboni hupata atomu ya hidrojeni na hidrojeni hutoka kwa uso mmoja wa uso wa palladium (chuma), karibu kila wakati watatoka kwa mwelekeo huo (kwa karatasi) na kila kaboni pia hupata kiungo kwa atomu ya chini ya electronegative (kaboni ya sp3 kutoka kaboni ya sp2). Hii ni kupunguzwa. Pia ni athari inayopendwa kwa sababu ni rahisi kukumbuka. Hata hivyo, usifanye kosa, hii ni athari ya kadi ya flash. Mambo mengine si rahisi kama hayo. Jambo ni kwamba hakuna utaratibu wa kuchora (hakuna mishale ya kushinikiza) hivyo watu ambao ni mpya upendo yake. Mmenyuko huu unaweza kujifunza na mwanafunzi wa shule ya sekondari ya msingi, kihalisi. Halogenation: Ni nini? au kufupishwa kwa njia hii: Kila kaboni ya kiungo cha mara mbili cha zamani (alkene) alipata kipengele cha electronegative. Kaboni zote mbili ni oxidized. Hii ni athari ya oksidi. Lakini si moja unaweza flashcard. Kama umekuwa alionyesha utaratibu (lavender mishale juu) una kufanya kazi ya tatizo kwa njia hiyo hiyo. Hakuna kadi za flash mpaka umeandika kutoka kumbukumbu angalau mara chache.