سلسلة متجانسة

فى الكيمياء, السلسة المتجانسة Homologous series هى سلسلة من المركبات العضوية لها نفس الخواص, وأعضاء هذه السلسلة تختلف بمقدار كتلة جزيئية ثابتة.

الألكانات (البرافينات), الألكينات (الأولفينات), الألكاينات (الاسيتيلينات) كلها تمثل سلاسل متجانسة يخنلف أعضائها بمقدار 14, 12, 10 وحدة من الكتل الرية على الترتيب. فمثلا, تبدأ سلسلة الألكانات بالميثان (CH₄), ثم الإيثان (C₂H₆), البروبان (C₃H₈), البيوتان (C₄H₁₀), البينتان (C₅H₁₂), وكل من هذه المركبات أعضاء في سلسلة الألكانات وكل منها يزيد عن المركب الذي يسبقه بمجموعة CH₂ (14 وحدة كتل ذرية).

المركبات الموجودة في كل سلسلة بها نفس المجموعة الصغيرة من الذرات التى تسمى المجموعة الفعالة. معظم الخواص الكيميائية للمركبات العضوية غالبا ما ترجع لهذه المجموعات الفعالة.

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أمثلة

The homologous series of straight-chained alkanes begins methane (CH₄), ethane (C₂H₆), propane (C₃H₈), butane (C₄H₁₀), and pentane (C₅H₁₂). In that series, successive members differ in mass by an extra methylene bridge (-CH₂- unit) inserted in the chain. Thus the molecular mass of each member differs by 14 atomic mass units. Adjacent members in such a series, such as methane and ethane, are known as "adjacent homologues".^[1]

Boiling points of alkanes versus number of carbon atoms

Normal boiling points of straight chain alkanes

Within that series, many physical properties such as boiling point gradually change with increasing mass. For example, ethane (C₂H₆), has a higher boiling point than methane (CH₄). This is because the London dispersion forces between ethane molecules are higher than that between methane molecules, resulting in stronger forces of intermolecular attraction, raising the boiling point.

Some important classes of organic molecules are derivatives of alkanes, such as the primary alcohols, aldehydes, and (mono)carboxylic acids form analogous series to the alkanes. The corresponding homologous series of primary straight-chained alcohols comprises methanol (CH₄O), ethanol (C₂H₆O), 1-propanol (C₃H₈O), 1-butanol, and so on. The single-ring cycloalkanes form another such series, starting with cyclopropane.

السلسلة المتجانسة	الصيغة العامة	الوحدة المتكررة	المجموعة الوظيفية
ألكانات السلاسل المستقيمة	C_nH_{2n + 2} (n ≥ 1)	−CH₂−	H₃C− ... −CH₃
Straight-chain perfluoroalkanes	C_nF_{2n + 2} (n ≥ 1)	−CF₂−	F₃C− ... −CF₃
Straight-chain alkyl	C_nH_{2n + 1} (n ≥ 1)	−CH₂−	H₃C− ... −CH₂−
1-ألكينات السلاسل المستقيمة	C_nH_2n (n ≥ 2)	−CH₂−	H₂C=C− ... −CH₃
ألكينات حلقية	C_nH_2n (n ≥ 2)	−CH₂−	Singly-bonded ring
Straight-chain 1-alkynes	C_nH_{2n − 2} (n ≥ 2)	−CH₂−	HC≡C− ... −CH₃
عديد الأسيتيلين	C_2nH_{2n + 2} (n ≥ 2)	−CH=CH−	H₃C− ... −CH₃
Straight-chain primary alcohols	C_nH_{2n + 1}OH (n ≥ 1)	−CH₂−	H₃C− ... −OH
Straight-chain primary monocarboxylic acids	C_nH_{2n + 1}COOH (n ≥ 0)	−CH₂−	H₃C− ... −COOH
Straight-chain azanes	N_nH_{n + 2} (n ≥ 1)	−NH−	H₂N− ... −NH₂

Biopolymers also form homologous series, for example the polymers of glucose such as cellulose oligomers^[2] starting with cellobiose, or the series of amylose oligomers starting with maltose, which are sometimes called maltooligomers.^[3] Homooligopeptides, oligopeptides made up of repetitions of only one amino acid can also be studied as homologous series.^[4]

السلسلة المتجانسة غير العضوية

Homologous series are not unique to organic chemistry. Titanium, vanadium, and molybdenum oxides all form homologous series (e.g. V_nO_{2n − 1} for 2 < n < 10), called Magnéli phases,^[5] as do the silanes, Si_nH_{2n + 2} (with n up to 8) that are analogous to the alkanes, C_nH_{2n + 2}.

انظر أيضاً

Ruddlesden-Popper phase

المصادر

^ See In re Henze, 181 F.2d 196, 201 (CCPA 1950), in which the court stated, "In effect, the nature of homologues and the close relationship the physical and chemical properties of one member of a series bears to adjacent members is such that a presumption of unpatentability arises against a claim directed to a composition of matter, the adjacent homologue of which is old in the art."
^ Rojas, Orlando J. (2016-02-25). Cellulose Chemistry and Properties: Fibers, Nanocelluloses and Advanced Materials (in الإنجليزية). Springer. ISBN 978-3-319-26015-0.
^ Advances in Carbohydrate Chemistry and Biochemistry (in الإنجليزية). Academic Press. 1981-06-19. ISBN 978-0-08-056297-1.
^ Giddings, J. Calvin (1982-08-25). Advances in Chromatography (in الإنجليزية). CRC Press. ISBN 978-0-8247-1868-8.
^ Schwingenschlögl, U.; Eyert, V. (2004-09-01). "The vanadium Magnéli phases V_nO_2n-1". Annalen der Physik (in الإنجليزية). 13 (9): 475–510. doi:10.1002/andp.200410099. ISSN 0003-3804.

[1] See In re Henze, 181 F.2d 196, 201 (CCPA 1950), in which the court stated, "In effect, the nature of homologues and the close relationship the physical and chemical properties of one member of a series bears to adjacent members is such that a presumption of unpatentability arises against a claim directed to a composition of matter, the adjacent homologue of which is old in the art."

[2] Rojas, Orlando J. (2016-02-25). Cellulose Chemistry and Properties: Fibers, Nanocelluloses and Advanced Materials (in الإنجليزية). Springer. ISBN 978-3-319-26015-0.

[3] Advances in Carbohydrate Chemistry and Biochemistry (in الإنجليزية). Academic Press. 1981-06-19. ISBN 978-0-08-056297-1.

[4] Giddings, J. Calvin (1982-08-25). Advances in Chromatography (in الإنجليزية). CRC Press. ISBN 978-0-8247-1868-8.

[5] Schwingenschlögl, U.; Eyert, V. (2004-09-01). "The vanadium Magnéli phases V_nO_2n-1". Annalen der Physik (in الإنجليزية). 13 (9): 475–510. doi:10.1002/andp.200410099. ISSN 0003-3804.

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