Tetramethylbutane

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| verifiedrevid = 401866579

| ImageFile = Tetramethylbutane skeletal.png

| ImageFile_Ref = {{chemboximage|correct|??}}

| ImageSize = 100

| ImageName = Skeletal formula of tetramethylbutane

| ImageFile1 = Tetramethylbutane 3D 1.png

| ImageFile1_Ref = {{chemboximage|correct|??}}

| ImageSize1 = 100

| ImageName1 = Spacefill model of tetramethylbutane

| PIN = 2,2,3,3-Tetramethylbutane{{Cite web|title=Hexamethylethane - Compound Summary|url=https://pubchem.ncbi.nlm.nih.gov/summary/summary.cgi?cid=11675&loc=ec_rcs|work=PubChem Compound|publisher=National Center for Biotechnology Information|accessdate=11 March 2012|location=USA|date=26 March 2005|at=Identification and Related Information}}

|Section1={{Chembox Identifiers

| CASNo = 594-82-1

| CASNo_Ref = {{cascite|correct|??}}

| UNII_Ref = {{fdacite|correct|FDA}}

| UNII = EB34RI15NY

| PubChem = 11675

| ChemSpiderID = 11185

| ChemSpiderID_Ref = {{chemspidercite|correct|chemspider}}

| EINECS = 209-855-6

| UNNumber = 1325

| SMILES = CC(C)(C)C(C)(C)C

| StdInChI = 1S/C8H18/c1-7(2,3)8(4,5)6/h1-6H3

| StdInChI_Ref = {{stdinchicite|correct|chemspider}}

| StdInChIKey = OMMLUKLXGSRPHK-UHFFFAOYSA-N

| StdInChIKey_Ref = {{stdinchicite|correct|chemspider}}

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|Section2={{Chembox Properties

| C=8 | H=18

| Appearance = White, opaque, waxy crystals

| Odor = Odorless

| MeltingPtK = 371 to 377

| BoilingPtK = 379.1 to 380.1

| HenryConstant = 2.9 nmol Pa⁻¹ kg⁻¹

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|Section3={{Chembox Thermochemistry

| DeltaHf = −270.3 – −267.9 kJ mol⁻¹

| DeltaHc = −5.4526 – −5.4504 MJ mol⁻¹

| Entropy = 273.76 J K⁻¹ mol⁻¹

| HeatCapacity = 232.2 J K⁻¹ mol⁻¹ (at 2.8 °C)

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|Section4={{Chembox Hazards

| GHSPictograms = {{GHS02}}{{GHS07}}{{GHS08}}{{GHS09}}

| GHSSignalWord = Danger

| HPhrases = {{H-phrases|228|304|315|336|410}}

| PPhrases = {{P-phrases|210|240|241|261|264|271|273|280|301+310|302+352|304+340|312|321|331|332+313|362|370+378|391|403+233|405|501}}

| FlashPtC = 4

| ExploLimits = 1–?%

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|Section5={{Chembox Related

| OtherFunction_label = alkanes

| OtherFunction = {{Unbulleted list|Neopentane|2,2-Dimethylbutane|2,3-Dimethylbutane|Triptane|Tetraethylmethane|2,2,4-Trimethylpentane|2,3,3-Trimethylpentane|2,3,4-Trimethylpentane|Tetra-tert-butylmethane}}

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Tetramethylbutane, sometimes called hexamethylethane, is a hydrocarbon with formula C₈H₁₈ or (H₃C-)₃C-C(-CH₃)₃. It is the most heavily branched and most compact of the octane isomers, the only one with a butane (C4) backbone. Because of its highly symmetrical structure, it has a very high melting point and a short liquid range; in fact, it is the smallest saturated acyclic hydrocarbon that appears as a solid at a room temperature of 25 °C. (Among cyclic hydrocarbons, cubane, C₈H₈, norbornane, C₇H₁₂ and norbornene, C₇H₁₀ are even smaller and are also solid at room temperature.) It is also the most stable C₈H₁₈ isomer, with a heat of formation {{convert|4.18|kcal/mol|kJ/mol|abbr=on}} lower than that of n-octane, a fact that has been attributed to stabilizing dispersive interactions (electron correlation) between the methyl groups (protobranching).{{Cite journal|last1=Joyce|first1=Justin P.|last2=Shores|first2=Matthew P.|last3=Rappè|first3=Anthony K.|date=2020-07-29|title=Protobranching as repulsion-induced attraction: a prototype for geminal stabilization|url=https://pubs.rsc.org/en/content/articlelanding/2020/cp/d0cp02193h|journal=Physical Chemistry Chemical Physics|language=en|volume=22|issue=29|pages=16998–17006|doi=10.1039/D0CP02193H|pmid=32676632 |bibcode=2020PCCP...2216998J |s2cid=220606477 |issn=1463-9084|url-access=subscription}}

The compound can be obtained from ethyl bromide, tert-butyl bromide, and magnesium metal in the presence of manganese(II) ions. Despite conditions amenable to the formation of a Grignard reagent, organomagnesium compounds are believed not to be the active species. Instead, they transmetalate to organomanganese compounds, which then decompose to tert-butyl radicals, which dimerize.{{cite journal |author1=M. S. KHARASCH |author2=J. W. HANCOCK |author3=W. NUDENBERG |author4=P. O. TAWNEY | year = 1956 | title = Factors Influencing the Course and Mechanism of Grignard Reactions. XXII. The Reaction of Grignard Reagents with Alkyl Halides and Ketones in the Presence of Manganous Salts | journal = Journal of Organic Chemistry | volume = 21 | issue = 3 | pages = 322–327 | doi=10.1021/jo01109a016}}

The full IUPAC name of the compound is 2,2,3,3-tetramethylbutane, but the numbers are superfluous in this case because there is no other possible arrangement of "tetramethylbutane".